Adding changelog entry

Signed-off-by: Ankit Jain <[email protected]>

Author: jainankitk

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Use Lucene `pack` method for `half_float` and `usigned_long` when using `ApproximatePointRangeQuery`.
 
 ### Changed
+- Combining filter rewrite and skip list to optimize sub aggregation([#19573](https://github.com/opensearch-project/OpenSearch/pull/19573))
 - Refactor to move prepareIndex and prepareDelete methods to Engine class ([#19551](https://github.com/opensearch-project/OpenSearch/pull/19551))
 
 ### Fixed