Adds 1.2.0.0 release notes (#67)

Signed-off-by: Surya Nistala <snistala@amazon.com>

Adds 1.2.0.0 release notes

Author: eirsep

release-notes/opensearch-asynchronous-search.release-notes-1.2.0.0.md

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+## Version 1.2.0.0 2021-11-05
+
+Compatible with OpenSearch 1.2.0
+
+### Bug Fixes
+
+* Add checkstyle plugin reference [#60](https://github.com/opensearch-project/asynchronous-search/pull/60)
+* Correct copyright notices to reflect Copyright OpenSearch Contributors [#61](https://github.com/opensearch-project/asynchronous-search/pull/61)
+
+
+### Infrastructure
+
+* Removes default integtest.sh [#36](https://github.com/opensearch-project/asynchronous-search/pull/36)
+* Updating CI workflows [#41](https://github.com/opensearch-project/asynchronous-search/pull/41)
+
+### Maintenance
+
+* Adds DCO check  [#57](https://github.com/opensearch-project/asynchronous-search/pull/57)
+* Incremented asynchronous search version to 1.2 [#53](https://github.com/opensearch-project/asynchronous-search/pull/53)
+
+