added release notes for 2.13

[sumukhswamy]

Description

added release notes for 2.13

Issues Resolved

[List any issues this PR will resolve]

Check List

• [ ] New functionality includes testing.
  • [ ] All tests pass, including unit test, integration test and doctest
• [ ] New functionality has been documented.
  • [ ] New functionality has javadoc added
  • [ ] New functionality has user manual doc added
• [ ] Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[ps48]

@sumukhswamy we need to update the bwc tests.

[rupal-bq]

@sumukhswamy we need to update the bwc tests.

CI failure is not related to this change. Raised another PR to fix CI https://github.com/opensearch-project/reporting/pull/977