[DOCS] Add 8.16.0 release notes (elastic#2283)

(cherry picked from commit 2b6c204)

Author: jbaiera

docs/src/reference/asciidoc/appendix/release-notes/8.16.0.adoc

@@ -0,0 +1,5 @@
+[[eshadoop-8.16.0]]
+== Elasticsearch for Apache Hadoop version 8.16.0
+
+ES-Hadoop 8.16.0 is a version compatibility release, tested specifically against
+Elasticsearch 8.16.0.

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-8.16.0>>
 * <<eshadoop-8.15.4>>
 * <<eshadoop-8.15.3>>
 * <<eshadoop-8.15.1>>
@@ -115,6 +116,7 @@ Elasticsearch 5.3.1.
 
 ////////////////////////
 
+include::release-notes/8.16.0.adoc[]
 include::release-notes/8.15.4.adoc[]
 include::release-notes/8.15.3.adoc[]
 include::release-notes/8.15.1.adoc[]