[DOCS] Add anchors for Asciidoctor migration (#41648)

Author: jrodewig

docs/reference/getting-started.asciidoc

@@ -375,6 +375,7 @@ This REST access pattern is pervasive throughout all the API commands that if yo
 Elasticsearch provides data manipulation and search capabilities in near real time. By default, you can expect a one second delay (refresh interval) from the time you index/update/delete your data until the time that it appears in your search results. This is an important distinction from other platforms like SQL wherein data is immediately available after a transaction is completed.
 
 [float]
+[[indexing-replacing-documents]]
 === Indexing/Replacing Documents
 
 We've previously seen how we can index a single document. Let's recall that command again:

docs/reference/modules/threadpool.asciidoc

@@ -78,6 +78,7 @@ The following are the types of thread pools that can be used and their
 respective parameters:
 
 [float]
+[[cache]]
 ==== `cache`
 
 The `cache` thread pool is an unbounded thread pool that will spawn a
@@ -92,6 +93,7 @@ threadpool:
 --------------------------------------------------
 
 [float]
+[[fixed]]
 ==== `fixed`
 
 The `fixed` thread pool holds a fixed size of threads to handle the
@@ -124,4 +126,4 @@ are wrongly detected, in such cases, the number of processors can be
 explicitly set using the `processors` setting.
 
 In order to check the number of processors detected, use the nodes info
-API with the `os` flag.
+API with the `os` flag.