Add release notes for 2.19.1 (#1385)

Author: Divyaasm

release-notes/opensearch-index-management.release-notes-2.19.1.0.md

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+## Version 2.19.1.0 2025-02-27
+
+Compatible with OpenSearch 2.19.1
+
+### Maintenance
+* CVE fix - Bump logback to 1.5.16 ([#1383](https://github.com/opensearch-project/index-management/pull/1383/files))