[DOCS] Adds the release notes for the 8.9.1 release. (elastic#163578)

## Summary

Adds the release notes for the 8.9.1 release.

Closes:elastic#163565
(cherry picked from commit 9bc2150)

docs/CHANGELOG.asciidoc

@@ -10,6 +10,7 @@
 
 Review important information about the {kib} 8.x releases.
 
+* <<release-notes-8.9.1>>
 * <<release-notes-8.9.0>>
 * <<release-notes-8.8.2>>
 * <<release-notes-8.8.1>>
@@ -45,6 +46,53 @@ Review important information about the {kib} 8.x releases.
 * <<release-notes-8.0.0-alpha1>>
 
 --
+[[release-notes-8.9.1]]
+== {kib} 8.9.1
+
+coming::[8.9.1]
+
+Review the following information about the {kib} 8.9.1 release. 
+
+[float]
+[[breaking-changes-8.9.1]]
+=== Breaking changes
+
+Breaking changes can prevent your application from optimal operation and performance.
+Before you upgrade to 8.9.0, review the breaking changes, then mitigate the impact to your application.
+
+There are no breaking changes in the {kib} 8.9.1 release.
+
+To review the breaking changes in the previous release, check {kibana-ref-all}/8.9/release-notes-8.9.0.html#breaking-changes-8.9.0[8.9.0].
+
+[float]
+[[fixes-v8.9.1]]
+=== Bug Fixes
+APM::
+* Fixes flame graph rendering on the transaction detail page ({kibana-pull}162968[#162968]).
+* Check if documents are missing `span.name` ({kibana-pull}162899[#162899]).
+* Fixes transaction action menu for Trace Explorer and dependency operations ({kibana-pull}162213[#162213]).
+Canvas::
+* Fixes embeddables not rendering in Canvas ({kibana-pull}163013[#163013]).
+Discover::
+* Fixes grid styles to enable better content wrapping ({kibana-pull}162325[#162325]).
+* Fixes search sessions using temporary data views ({kibana-pull}161029[#161029]).
+* Make share links and search session information shorter for temporary data views ({kibana-pull}161180[#161180]).
+Elastic Security::
+For the Elastic Security 8.9.1 release information, refer to {security-guide}/release-notes.html[_Elastic Security Solution Release Notes_].
+Fleet::
+* Fixes for query error on Agents list in the UI ({kibana-pull}162816[#162816]).
+* Remove duplicate path being pushed to package archive ({kibana-pull}162724[#162724]).
+Management::
+* Resolves potential errors present in v8.9.0 with data views that contain field filters that have been edited ({kibana-pull}162860[#162860]).
+Uptime::
+* Fixes Monitor not found 404 message display ({kibana-pull}163501[#163501]).
+
+[float]
+[[enhancement-v8.9.1]]
+=== Enhancements
+Discover::
+* Set legend width to extra large and enable text wrapping in legend labels ({kibana-pull}163009[#163009]).
+
 [[release-notes-8.9.0]]
 == {kib} 8.9.0