[Backport 2.15] Add release notes for 2.15 (#1192)

(cherry picked from commit 52f331f)

Signed-off-by: vikasvb90 <[email protected]>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
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-2.15.0.0.md

@@ -0,0 +1,7 @@
+## Version 2.15.0.0 2024-06-14
+
+Compatible with OpenSearch 2.15.0
+
+### Bug fixes
+
+* Step Metadata Update on Index Rollover Timeout ([#1174](https://github.com/opensearch-project/index-management/pull/1174))