Add 2.9.1 to BWC and known versions

[reta]

Description

Fix broken BWC tests after #8897

Related Issues

N/A

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

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.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/21090/
• CommitID: 4aa2901

[codecov]

Codecov Report

Merging #8923 (4aa2901) into 2.x (1eea7fd) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##                2.x    #8923      +/-   ##
============================================
+ Coverage     70.78%   70.81%   +0.03%     
- Complexity    57326    57328       +2     
============================================
  Files          4745     4745              
  Lines        271063   271064       +1     
  Branches      39981    39981              
============================================
+ Hits         191862   191950      +88     
+ Misses        62770    62606     -164     
- Partials      16431    16508      +77     

Files Changed	Coverage Δ
...ibs/core/src/main/java/org/opensearch/Version.java	83.25% <100.00%> (+0.51%)	⬆️

... and 444 files with indirect coverage changes

[kotwanikunal]

Thanks @reta !

[kotwanikunal]

@reta Does this need to go to main as well?

[opensearch-trigger-bot]

The backport to main failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-main main
# Navigate to the new working tree
pushd ../.worktrees/backport-main
# Create a new branch
git switch --create backport/backport-8923-to-main
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 212dba457d6b2d540694e040a0485529d6e52e12
# Push it to GitHub
git push --set-upstream origin backport/backport-8923-to-main
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-main

Then, create a pull request where the base branch is main and the compare/head branch is backport/backport-8923-to-main.

[reta]

@reta Does this need to go to main as well?

Yes! Doing just that