add CHANGELOG entry

Signed-off-by: Kaushal Kumar <[email protected]>

Author: kaushalmahi12

CHANGELOG.md

@@ -42,6 +42,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fix exists queries on nested flat_object fields throws exception ([#16803](https://github.com/opensearch-project/OpenSearch/pull/16803))
 - Add highlighting for wildcard search on `match_only_text` field ([#17101](https://github.com/opensearch-project/OpenSearch/pull/17101))
 - Fix illegal argument exception when creating a PIT ([#16781](https://github.com/opensearch-project/OpenSearch/pull/16781))
+- Fix NPE in node stats due to QueryGroupTasks ([#17576](https://github.com/opensearch-project/OpenSearch/pull/17576))
 
 ### Security