Documentation update.

Original Pull Request #2584
Closes #2583

Author: sothawo

src/main/asciidoc/reference/elasticsearch-new.adoc

@@ -5,6 +5,9 @@
 == New in Spring Data Elasticsearch 5.2
 
 * Upgrade to Elasticsearch 8.8.0
+* The `JsonpMapper` for Elasticsearch is now configurable and provided as bean.
+* Improved AOT runtime hints for Elasticsearch client library classes.
+* Add Kotlin extensions and repository coroutine support.
 
 [[new-features.5-1-0]]
 == New in Spring Data Elasticsearch 5.1