[DOCS] Adds breaking changes page with content re-use

Author: lcawl

docs/en/install-upgrade/breaking.asciidoc

@@ -0,0 +1,27 @@
+[[elastic-stack-breaking-changes]]
+== Breaking changes
+
+Before you upgrade, you must review the breaking changes for each product you
+use and make the necessary changes so your code is compatible with {version}. 
+
+** {beats-ref}/breaking-changes.html[Beats {version} breaking changes]
+** {apm-server-ref}/breaking-changes.html[APM Server {version} breaking changes]
+** {ref}/breaking-changes.html[Elasticsearch {version} breaking changes]
+** {hadoop-ref}/breaking-changes.html[Elasticsearch Hadoop {version} breaking changes]
+** {kibana-ref}/breaking-changes.html[Kibana {version} breaking changes]
+** {logstash-ref}/breaking-changes.html[Logstash {version} breaking changes]
+
+[IMPORTANT]
+===============================
+
+* If you're upgrading from 2.n, make sure you check the breaking changes from
+2.n to 5.n, as well as from 5.n to 6.n!
+* If you are using {ml} {dfeeds} that contain discontinued search or query
+domain specific language (DSL), the upgrade will fail. In 5.6.5 and later, the
+Upgrade Assistant provides information about which {dfeeds} need to be updated.
+
+===============================
+
+ifdef::asciidoctor-builds[]
+include::{es-repo-dir}/reference/migration/migrate_7_0.asciidoc[tag=notable-breaking-changes]
+endif::asciidoctor-builds[]

docs/index.asciidoc

@@ -1,8 +1,11 @@
 [[elastic-stack]]
 = Elastic Stack
 
+:asciidoctor-builds: true
+:es-repo-dir:        {docdir}/../../elasticsearch/docs
+
 include::{asciidoc-dir}/../../shared/attributes.asciidoc[]
-include::{docdir}/../../elasticsearch/docs/Versions.asciidoc[]
+include::{es-repo-dir}/Versions.asciidoc[]
 
 == Overview
 
@@ -31,5 +34,4 @@ include::installing-stack.asciidoc[]
 
 include::upgrading-stack.asciidoc[]
 
-
-
+include::en/install-upgrade/breaking.asciidoc[]