[DOCS] Adds changelog to Elasticsearch Reference (#30271)

docs/CHANGELOG.asciidoc

@@ -1,12 +1,26 @@
+[[es-release-notes]]
+= {es} Release Notes
+
+[partintro]
+--
 // Use these for links to issue and pulls. Note issues and pulls redirect one to
 // each other on Github, so don't worry too much on using the right prefix.
 :issue: https://github.com/elastic/elasticsearch/issues/
 :pull: https://github.com/elastic/elasticsearch/pull/
 
-= Elasticsearch Release Notes
+This section summarizes the changes in each release.
 
-== Elasticsearch 7.0.0
+* <<release-notes-7.0.0>>
+* <<release-notes-6.4.0>>
 
+
+--
+
+[[release-notes-7.0.0]]
+== {es} 7.0.0
+
+[float]
+[[breaking-7.0.0]]
 === Breaking Changes
 
 <<write-thread-pool-fallback, Removed `thread_pool.bulk.*` settings and
@@ -16,37 +30,48 @@
 
 <<remove-field-caps-body, In field capabilities APIs, removed support for providing fields in the request body>> ({pull}30185[#30185])
 
-=== Breaking Java Changes
+//[float]
+//=== Breaking Java Changes
 
-=== Deprecations
+//[float]
+//=== Deprecations
 
-=== New Features
+//[float]
+//=== New Features
 
-=== Enhancements
+//[float]
+//=== Enhancements
 
+[float]
 === Bug Fixes
 
 Fail snapshot operations early when creating or deleting a snapshot on a repository that has been
 written to by an older Elasticsearch after writing to it with a newer Elasticsearch version. ({pull}30140[#30140])
 
-=== Regressions
+//[float]
+//=== Regressions
 
-=== Known Issues
+//[float]
+//=== Known Issues
 
-== Elasticsearch version 6.4.0
+[[release-notes-6.4.0]]
+== {es} 6.4.0
 
-=== New Features
+//[float]
+//=== New Features
 
+[float]
 === Enhancements
 
 <<copy-source-settings-on-resize, Allow copying source settings on index resize operations>> ({pull}30255[#30255])
 
+[float]
 === Bug Fixes
 
 Do not ignore request analysis/similarity settings on index resize operations when the source index already contains such settings ({pull}30216[#30216])
 
-=== Regressions
-
-=== Known Issues
-
+//[float]
+//=== Regressions
 
+//[float]
+//=== Known Issues

docs/reference/index-shared4.asciidoc

@@ -5,4 +5,4 @@ include::testing.asciidoc[]
 
 include::glossary.asciidoc[]
 
-include::release-notes.asciidoc[]
+include::{docdir}/../CHANGELOG.asciidoc[]

x-pack/docs/en/release-notes/7.0.0-alpha1.asciidoc

@@ -21,6 +21,5 @@ ones that the user is authorized to access in case field level security is enabl
 
 See also:
 
-* <<release-notes-7.0.0-alpha1,{es} 7.0.0-alpha1 Release Notes>>
 * {kibana-ref}/xkb-7.0.0-alpha1.html[{kib} {xpack} 7.0.0-alpha1 Release Notes]
 * {logstash-ref}/xls-7.0.0-alpha1.html[Logstash {xpack} 7.0.0-alpha1 Release Notes]