[Backport 2.x] Clear out 2.x section of changelog

[andrross]

The 2.13 release notes have been created.

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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[github-actions]

Compatibility status:

Checks if related components are compatible with change 6a690c9

Incompatible components

Skipped components

Compatible components

Compatible components: [https://github.com/opensearch-project/custom-codecs.git, https://github.com/opensearch-project/observability.git, https://github.com/opensearch-project/flow-framework.git, https://github.com/opensearch-project/job-scheduler.git, https://github.com/opensearch-project/cross-cluster-replication.git, https://github.com/opensearch-project/geospatial.git, https://github.com/opensearch-project/neural-search.git, https://github.com/opensearch-project/k-nn.git, https://github.com/opensearch-project/sql.git, https://github.com/opensearch-project/security-analytics.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/alerting.git, https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/performance-analyzer.git]

[github-actions]

❌ Gradle check result for a115ce4:

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for a115ce4: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[reta]

❌ Gradle check result for a115ce4: FAILURE

#5257
#10762

[github-actions]

❌ Gradle check result for a115ce4: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for a115ce4: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[reta]

@andrross could you rebase please? thank you

[github-actions]

✅ Gradle check result for 284f19e: SUCCESS

[github-actions]

❕ Gradle check result for 6a690c9: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.cluster.MinimumClusterManagerNodesIT.testThreeNodesNoClusterManagerBlock

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.14%. Comparing base (0dd892c) to head (6a690c9).
Report is 83 commits behind head on 2.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #12869      +/-   ##
============================================
- Coverage     71.28%   71.14%   -0.14%     
- Complexity    60145    60416     +271     
============================================
  Files          4957     4985      +28     
  Lines        282799   284400    +1601     
  Branches      41409    41582     +173     
============================================
+ Hits         201591   202345     +754     
- Misses        64189    64972     +783     
- Partials      17019    17083      +64     

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