Added Release notes for 2.15 (#926)

* Added release notes for 2.15.0

Signed-off-by: Riya Saxena <riysaxen@amazon.com>

* Added release notes for 2.15.0

Signed-off-by: Riya Saxena <riysaxen@amazon.com>

---------

Signed-off-by: Riya Saxena <riysaxen@amazon.com>

Author: riysaxen-amzn

release-notes/opensearch-notifications.release-notes-2.15.0.0.md

@@ -0,0 +1,10 @@
+## Version 2.15.0.0 2024-06-10
+
+Compatible with OpenSearch 2.15.0
+
+### Maintenance
+* Increment version to 2.15.0-SNAPSHOT (#[918](https://github.com/opensearch-project/notifications/pull/918))
+
+### Documentation
+* Add 2.15.0 release notes (#[926](https://github.com/opensearch-project/notifications/pull/926))
+