[DOCS] Add 8.12.1 release notes (#2195)

Author: jbaiera

docs/src/reference/asciidoc/appendix/release-notes/8.12.1.adoc

@@ -0,0 +1,5 @@
+[[eshadoop-8.12.1]]
+== Elasticsearch for Apache Hadoop version 8.12.1
+
+ES-Hadoop 8.12.1 is a version compatibility release, tested specifically against
+Elasticsearch 8.12.1.

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-8.12.1>>
 * <<eshadoop-8.12.0>>
 * <<eshadoop-8.11.4>>
 * <<eshadoop-8.11.3>>
@@ -100,6 +101,7 @@ Elasticsearch 5.3.1.
 
 ////////////////////////
 
+include::release-notes/8.12.1.adoc[]
 include::release-notes/8.12.0.adoc[]
 include::release-notes/8.11.4.adoc[]
 include::release-notes/8.11.3.adoc[]