Add changelog

Signed-off-by: Sooraj Sinha <[email protected]>

Author: soosinha

CHANGELOG.md

@@ -62,6 +62,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Enable coordinator search.request_stats_enabled by default ([#16290](https://github.com/opensearch-project/OpenSearch/pull/16290))
 - Code cleanup: Remove ApproximateIndexOrDocValuesQuery ([#16273](https://github.com/opensearch-project/OpenSearch/pull/16273))
 - Optimise clone operation for incremental full cluster snapshots ([#16296](https://github.com/opensearch-project/OpenSearch/pull/16296))
+- Update last seen cluster state in the commit phase ([#16215](https://github.com/opensearch-project/OpenSearch/pull/16215))
 
 ### Deprecated