[8.10] [DOCS] Add 8.9.1 release notes (#2122) (#2124)

Co-authored-by: James Baiera <[email protected]>

Author: jrodewig

docs/src/reference/asciidoc/appendix/release-notes/8.9.1.adoc

@@ -0,0 +1,5 @@
+[[eshadoop-8.9.1]]
+== Elasticsearch for Apache Hadoop version 8.9.1
+
+ES-Hadoop 8.9.1 is a version compatibility release, tested specifically against
+Elasticsearch 8.9.1.

docs/src/reference/asciidoc/appendix/release.adoc

@@ -9,6 +9,7 @@ This section summarizes the changes in each release.
 [[release-notes-8]]
 ===== 8.x
 
+* <<eshadoop-8.9.1>>
 * <<eshadoop-8.9.0>>
 * <<eshadoop-8.8.2>>
 * <<eshadoop-8.8.1>>
@@ -87,6 +88,7 @@ Elasticsearch 5.3.1.
 
 ////////////////////////
 
+include::release-notes/8.9.1.adoc[]
 include::release-notes/8.9.0.adoc[]
 include::release-notes/8.8.2.adoc[]
 include::release-notes/8.8.1.adoc[]