Bumping 2.x to 2.8.0

[Rishikesh1159]

Description

This PR bumps 2.x to 2.8.0

Issues Resolved

#6967

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: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.indices.replication.SegmentReplicationIT.testScrollCreatedOnReplica
      1 org.opensearch.backwards.MixedClusterClientYamlTestSuiteIT.test {p0=pit/10_basic/Delete all}

• URL: https://build.ci.opensearch.org/job/gradle-check/14255/
• CommitID: 5e72e61
  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-commenter]

Codecov Report

Merging #7237 (5e72e61) into 2.x (09bc5e1) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

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@@             Coverage Diff              @@
##                2.x    #7237      +/-   ##
============================================
- Coverage     70.33%   70.31%   -0.02%     
+ Complexity    59699    59682      -17     
============================================
  Files          4847     4847              
  Lines        287115   287116       +1     
  Branches      41716    41716              
============================================
- Hits         201935   201895      -40     
- Misses        68299    68343      +44     
+ Partials      16881    16878       -3     

Impacted Files	Coverage Δ
server/src/main/java/org/opensearch/Version.java	83.84% <100.00%> (+0.50%)	⬆️
...ing/allocation/allocator/RemoteShardsBalancer.java	51.07% <100.00%> (ø)

... and 503 files with indirect coverage changes

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