[DOCS] Remove heading offsets for REST APIs (#44568)

Several files in the REST APIs nav section are included using
:leveloffset: tags. This increments headings (h2 -> h3, h3 -> h4, etc.)
in those files and removes the :leveloffset: tags.

Other supporting changes:
* Alphabetizes top-level REST API nav items.
* Change 'indices APIs' heading to 'index APIs.'
* Changes 'Snapshot lifecycle management' heading to sentence case.

Author: jrodewig

docs/reference/api-conventions.asciidoc

@@ -1,5 +1,5 @@
 [[api-conventions]]
-= API conventions
+== API conventions
 
 The *Elasticsearch* REST APIs are exposed using <<modules-http,JSON over HTTP>>.
 
@@ -12,7 +12,7 @@ API, unless otherwise specified.
 * <<url-access-control>>
 
 [[multi-index]]
-== Multiple Indices
+=== Multiple Indices
 
 Most APIs that refer to an `index` parameter support execution across multiple indices,
 using simple `test1,test2,test3` notation (or `_all` for all indices). It also
@@ -55,7 +55,7 @@ NOTE: Single index APIs such as the <<docs>> and the
 <<indices-aliases,single-index `alias` APIs>> do not support multiple indices.
 
 [[date-math-index-names]]
-== Date math support in index names
+=== Date math support in index names
 
 Date math index name resolution enables you to search a range of time-series indices, rather
 than searching all of your time-series indices and filtering the results or maintaining aliases.
@@ -164,12 +164,12 @@ GET /%3Clogstash-%7Bnow%2Fd-2d%7D%3E%2C%3Clogstash-%7Bnow%2Fd-1d%7D%3E%2C%3Clogs
 // TEST[s/now/2016.09.20||/]
 
 [[common-options]]
-== Common options
+=== Common options
 
 The following options can be applied to all of the REST APIs.
 
 [float]
-=== Pretty Results
+==== Pretty Results
 
 When appending `?pretty=true` to any request made, the JSON returned
 will be pretty formatted (use it for debugging only!). Another option is
@@ -178,7 +178,7 @@ to set `?format=yaml` which will cause the result to be returned in the
 
 
 [float]
-=== Human readable output
+==== Human readable output
 
 Statistics are returned in a format suitable for humans
 (e.g. `"exists_time": "1h"` or `"size": "1kb"`) and for computers
@@ -191,7 +191,7 @@ consumption.  The default for the `human` flag is
 
 [[date-math]]
 [float]
-=== Date Math
+==== Date Math
 
 Most parameters which accept a formatted date value -- such as `gt` and `lt`
 in <<query-dsl-range-query,`range` queries>>, or `from` and `to`
@@ -229,7 +229,7 @@ Assuming `now` is `2001-01-01 12:00:00`, some examples are:
 
 [float]
 [[common-options-response-filtering]]
-=== Response Filtering
+==== Response Filtering
 
 All REST APIs accept a `filter_path` parameter that can be used to reduce
 the response returned by Elasticsearch. This parameter takes a comma
@@ -396,7 +396,7 @@ GET /_search?filter_path=hits.hits._source&_source=title&sort=rating:desc
 
 
 [float]
-=== Flat Settings
+==== Flat Settings
 
 The `flat_settings` flag affects rendering of the lists of settings. When the 
 `flat_settings` flag is `true`, settings are returned in a flat format:
@@ -467,27 +467,27 @@ Returns:
 By default `flat_settings` is set to `false`.
 
 [float]
-=== Parameters
+==== Parameters
 
 Rest parameters (when using HTTP, map to HTTP URL parameters) follow the
 convention of using underscore casing.
 
 [float]
-=== Boolean Values
+==== Boolean Values
 
 All REST API parameters (both request parameters and JSON body) support
 providing boolean "false" as the value `false` and boolean "true" as the
 value `true`. All other values will raise an error.
 
 [float]
-=== Number Values
+==== Number Values
 
 All REST APIs support providing numbered parameters as `string` on top
 of supporting the native JSON number types.
 
 [[time-units]]
 [float]
-=== Time units
+==== Time units
 
 Whenever durations need to be specified, e.g. for a `timeout` parameter, the duration must specify
 the unit, like `2d` for 2 days.  The supported units are:
@@ -503,7 +503,7 @@ the unit, like `2d` for 2 days.  The supported units are:
 
 [[byte-units]]
 [float]
-=== Byte size units
+==== Byte size units
 
 Whenever the byte size of data needs to be specified, e.g. when setting a buffer size
 parameter, the value must specify the unit, like `10kb` for 10 kilobytes. Note that
@@ -519,7 +519,7 @@ these units use powers of 1024, so `1kb` means 1024 bytes. The supported units a
 
 [[size-units]]
 [float]
-=== Unit-less quantities
+==== Unit-less quantities
 
 Unit-less quantities means that they don't have a "unit" like "bytes" or "Hertz" or "meter" or "long tonne".
 
@@ -535,7 +535,7 @@ when we mean 87 though. These are the supported multipliers:
 
 [[distance-units]]
 [float]
-=== Distance Units
+==== Distance Units
 
 Wherever distances need to be specified, such as the `distance` parameter in
 the <<query-dsl-geo-distance-query>>), the default unit is meters if none is specified.
@@ -557,7 +557,7 @@ Nautical mile:: `NM`, `nmi`, or `nauticalmiles`
 
 [[fuzziness]]
 [float]
-=== Fuzziness
+==== Fuzziness
 
 Some queries and APIs support parameters to allow inexact _fuzzy_ matching,
 using the `fuzziness` parameter.
@@ -590,7 +590,7 @@ the default values are 3 and 6, equivalent to `AUTO:3,6` that make for lengths:
 
 [float]
 [[common-options-error-options]]
-=== Enabling stack traces
+==== Enabling stack traces
 
 By default when a request returns an error Elasticsearch doesn't include the
 stack trace of the error. You can enable that behavior by setting the
@@ -668,7 +668,7 @@ The response looks like:
 // TESTRESPONSE[s/"stack_trace": "java.lang.Number.+\.\.\."/"stack_trace": $body.error.caused_by.stack_trace/]
 
 [float]
-=== Request body in query string
+==== Request body in query string
 
 For libraries that don't accept a request body for non-POST requests,
 you can pass the request body as the `source` query string parameter
@@ -677,7 +677,7 @@ should also be passed with a media type value that indicates the format
 of the source, such as `application/json`.
 
 [float]
-=== Content-Type Requirements
+==== Content-Type Requirements
 
 The type of the content sent in a request body must be specified using
 the `Content-Type` header. The value of this header must map to one of
@@ -690,7 +690,7 @@ content type must be specified using the `source_content_type` query
 string parameter.
 
 [[url-access-control]]
-== URL-based access control
+=== URL-based access control
 
 Many users use a proxy with URL-based access control to secure access to
 Elasticsearch indices. For <<search-multi-search,multi-search>>,

docs/reference/cat.asciidoc

@@ -1,8 +1,8 @@
 [[cat]]
-= cat APIs
+== cat APIs
 
 ["float",id="intro"]
-== Introduction
+=== Introduction
 
 JSON is great... for computers.  Even if it's pretty-printed, trying
 to find relationships in the data is tedious.  Human eyes, especially
@@ -15,11 +15,11 @@ the available commands.
 
 [float]
 [[common-parameters]]
-== Common parameters
+=== Common parameters
 
 [float]
 [[verbose]]
-=== Verbose
+==== Verbose
 
 Each of the commands accepts a query string parameter `v` to turn on
 verbose output. For example:
@@ -41,7 +41,7 @@ u_n93zwxThWHi1PDBJAGAg 127.0.0.1 127.0.0.1 u_n93zw
 
 [float]
 [[help]]
-=== Help
+==== Help
 
 Each of the commands accepts a query string parameter `help` which will
 output its available columns. For example:
@@ -70,7 +70,7 @@ instead.
 
 [float]
 [[headers]]
-=== Headers
+==== Headers
 
 Each of the commands accepts a query string parameter `h` which forces
 only those columns to appear. For example:
@@ -95,7 +95,7 @@ with `queue`.
 
 [float]
 [[numeric-formats]]
-=== Numeric formats
+==== Numeric formats
 
 Many commands provide a few types of numeric output, either a byte, size
 or a time value.  By default, these types are human-formatted,
@@ -126,7 +126,7 @@ If you want to change the <<size-units,size units>>, use `size` parameter.
 If you want to change the <<byte-units,byte units>>, use `bytes` parameter.
 
 [float]
-=== Response as text, json, smile, yaml or cbor
+==== Response as text, json, smile, yaml or cbor
 
 [source,sh]
 --------------------------------------------------
@@ -179,7 +179,7 @@ For example:
 
 [float]
 [[sort]]
-=== Sort
+==== Sort
 
 Each of the commands accepts a query string parameter `s` which sorts the table by
 the columns specified as the parameter value. Columns are specified either by name or by

docs/reference/cat/alias.asciidoc

@@ -1,5 +1,5 @@
 [[cat-alias]]
-== cat aliases
+=== cat aliases
 
 `aliases` shows information about currently configured aliases to indices
 including filter and routing infos.

docs/reference/cat/allocation.asciidoc

@@ -1,5 +1,5 @@
 [[cat-allocation]]
-== cat allocation
+=== cat allocation
 
 `allocation` provides a snapshot of how many shards are allocated to each data node
 and how much disk space they are using.

docs/reference/cat/count.asciidoc

@@ -1,5 +1,5 @@
 [[cat-count]]
-== cat count
+=== cat count
 
 `count` provides quick access to the document count of the entire
 cluster, or individual indices.

docs/reference/cat/fielddata.asciidoc

@@ -1,5 +1,5 @@
 [[cat-fielddata]]
-== cat fielddata
+=== cat fielddata
 
 `fielddata` shows how much heap memory is currently being used by fielddata
 on every data node in the cluster.

docs/reference/cat/health.asciidoc

@@ -1,5 +1,5 @@
 [[cat-health]]
-== cat health
+=== cat health
 
 `health` is a terse, one-line representation of the same information
 from `/_cluster/health`.
@@ -75,7 +75,7 @@ static, we would have an idea that there is a problem.
 
 [float]
 [[timestamp]]
-=== Why the timestamp?
+==== Why the timestamp?
 
 You typically are using the `health` command when a cluster is
 malfunctioning.  During this period, it's extremely important to

docs/reference/cat/indices.asciidoc

@@ -1,5 +1,5 @@
 [[cat-indices]]
-== cat indices
+=== cat indices
 
 The `indices` command provides a cross-section of each index.  This
 information *spans nodes*. For example:
@@ -37,15 +37,15 @@ is to use either the <<cat-count>> or the <<search-count>>
 
 [float]
 [[pri-flag]]
-=== Primaries
+==== Primaries
 
 The index stats by default will show them for all of an index's
 shards, including replicas.  A `pri` flag can be supplied to enable
 the view of relevant stats in the context of only the primaries.
 
 [float]
 [[examples]]
-=== Examples
+==== Examples
 
 Which indices are yellow?
 

docs/reference/cat/master.asciidoc

@@ -1,5 +1,5 @@
 [[cat-master]]
-== cat master
+=== cat master
 
 `master` doesn't have any extra options. It simply displays the
 master's node ID, bound IP address, and node name. For example:

docs/reference/cat/nodeattrs.asciidoc

@@ -1,5 +1,5 @@
 [[cat-nodeattrs]]
-== cat nodeattrs
+=== cat nodeattrs
 
 The `nodeattrs` command shows custom node attributes.
 For example:
@@ -32,7 +32,7 @@ and the `attr` and `value` columns give you the custom node attributes,
 one per line.
 
 [float]
-=== Columns
+==== Columns
 
 Below is an exhaustive list of the existing headers that can be
 passed to `nodeattrs?h=` to retrieve the relevant details in ordered