Add Changelog

Signed-off-by: Mingshi Liu <mingshl@amazon.com>

CHANGELOG.md

@@ -11,7 +11,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add events correlation engine plugin ([#6854](https://github.com/opensearch-project/OpenSearch/issues/6854))
 - Add support for ignoring missing Javadoc on generated code using annotation ([#7604](https://github.com/opensearch-project/OpenSearch/pull/7604))
 - Implement concurrent aggregations support without profile option ([#7514](https://github.com/opensearch-project/OpenSearch/pull/7514))
-
+- Enable Partial Flat Object ([#7997](https://github.com/opensearch-project/OpenSearch/pull/7997))
+-
 ### Dependencies
 - Bump `log4j-core` from 2.18.0 to 2.19.0
 - Bump `forbiddenapis` from 3.3 to 3.4