Changelog entry

Signed-off-by: Kartik Ganesh <gkart@amazon.com>

CHANGELOG.md

@@ -11,6 +11,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Prevent deletion of snapshots that are backing searchable snapshot indexes ([#5069](https://github.com/opensearch-project/OpenSearch/pull/5069))
 - Update to Gradle 7.6 ([#5382](https://github.com/opensearch-project/OpenSearch/pull/5382))
 - Reject bulk requests with invalid actions ([#5299](https://github.com/opensearch-project/OpenSearch/issues/5299))
+- Experimental support for extended backward compatiblity in searchable snapshots ([#5429](https://github.com/opensearch-project/OpenSearch/pull/5429))
 ### Dependencies
 - Bump bcpg-fips from 1.0.5.1 to 1.0.7.1 ([#5148](https://github.com/opensearch-project/OpenSearch/pull/5148))
 - Bumps `commons-compress` from 1.21 to 1.22 ([#5104](https://github.com/opensearch-project/OpenSearch/pull/5104))