Update branch to 1.2 and add release notes (#99)

Signed-off-by: Sruti Parthiban <[email protected]>

Author: sruti1312

release-notes/opensearch-performance-analyzer.release-notes-1.2.1.0.md

@@ -0,0 +1,12 @@
+## Version 1.2.1.0 Release Notes
+
+Compatible with OpenSearch 1.2.1
+
+### Bug fixes
+
+* Upgrade plugin and log4j version ([#96](https://github.com/opensearch-project/performance-analyzer-rca/pull/96))
+* Upgrade plugin and log4j version ([#98](https://github.com/opensearch-project/performance-analyzer/pull/98))
+
+### Maintenance
+
+* Update branch to 1.2 and add release notes ([#99](https://github.com/opensearch-project/performance-analyzer/pull/99))