[Backport 2.16] 2.16 Release Notes (#1216)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

release-notes/opensearch-index-management.release-notes-2.16.0.0.md

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+## Version 2.16.0.0 2024-07-29
+
+Compatible with OpenSearch 2.16.0
+
+### Maintenance
+* Increment version to 2.16.0-SNAPSHOT ([#1187](https://github.com/opensearch-project/index-management/pull/1187))
+* Add publish in spi build.gradle ([#1207](https://github.com/opensearch-project/index-management/pull/1207))
+* Fix github action ([#1208](https://github.com/opensearch-project/index-management/pull/1208))