Added Release Notes for v 3.1.0 (#1324)

Signed-off-by: Vaibhav Agarwal <vaibhoag@amazon.com>

Author: vaibhoag

release-notes/opensearch-index-management-dashboards-plugin.release-notes-3.1.0.0.md

@@ -0,0 +1,7 @@
+## Version 3.1.0.0 2025-06-16
+
+Compatible with OpenSearch 3.1.0
+
+### Maintenance
+* Increment version to 3.1.0.0 ([#1313](https://github.com/opensearch-project/index-management-dashboards-plugin/pull/1313))
+* Updated @testing-library/user-event dependency ([#1321](https://github.com/opensearch-project/index-management-dashboards-plugin/pull/1321))