[DOCS] Add 8.4.2 release notes (#1998) (#1999)

(cherry picked from commit b8fec87)

Author: jbaiera

docs/src/reference/asciidoc/appendix/release-notes/8.4.2.adoc

@@ -0,0 +1,5 @@
+[[eshadoop-8.4.2]]
+== Elasticsearch for Apache Hadoop version 8.4.2
+
+ES-Hadoop 8.4.2 is a version compatibility release, tested specifically against
+Elasticsearch 8.4.2.

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-8.4.2>>
 * <<eshadoop-8.4.1>>
 * <<eshadoop-8.4.0>>
 * <<eshadoop-8.3.3>>
@@ -72,6 +73,7 @@ Elasticsearch 5.3.1.
 
 ////////////////////////
 
+include::release-notes/8.4.2.adoc[]
 include::release-notes/8.4.1.adoc[]
 include::release-notes/8.4.0.adoc[]
 include::release-notes/8.3.3.adoc[]