update changelog

Signed-off-by: Nicholas Walter Knize <nknize@apache.org>

Author: nknize

CHANGELOG.md

@@ -55,6 +55,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Allow insecure string settings to warn-log usage and advise to migration of a newer secure variant ([#5496](https://github.com/opensearch-project/OpenSearch/pull/5496))
 - Pass localNode info to all plugins on node start ([#7919](https://github.com/opensearch-project/OpenSearch/pull/7919)
 - Compress and cache cluster state during validate join request ([#7321](https://github.com/opensearch-project/OpenSearch/pull/7321))
+- [Refactor] ClusterInfo to use j.util.Map instead of ImmutableOpenMap ([#7126](https://github.com/opensearch-project/OpenSearch/pull/7126))
 
 ### Deprecated