[Backport 2.x] Add connectToNodeAsExtension in TransportService

[cwperks]

Backport #6866 to 2.x

[owaiskazi19]

Why are we adding these changes to CHANGELOG? They have already been released in 2.7.
Just the below change should be enough for this PR.

[owaiskazi19]

Also, I think this was missed during the review of #6866 . Since we are backporting it to 2.x and it will be released in 2.8 we don't need to add the CHANGELOG entry under unreleased 3.x but rather unreleased 2.x. This was the reason of the failed backport workflow. I would suggest to raise another PR on main and add the change under 2.x and remove it from 3.x.

[cwperks]

Updated, I used the merge conflict tool on github when resolving the conflict. I'm not sure how all of the other items got included.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/14706/
• CommitID: a5a2cff
  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 (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.indices.replication.SegmentReplicationIT.testScrollWithOngoingSegmentReplication

• URL: https://build.ci.opensearch.org/job/gradle-check/14707/
• CommitID: 5f8e7b0
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      2 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString
      1 org.opensearch.backwards.MixedClusterClientYamlTestSuiteIT.test {p0=pit/10_basic/Delete all}

• URL: https://build.ci.opensearch.org/job/gradle-check/14708/
• CommitID: 061cd05
  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 #7346 (061cd05) into 2.x (59d59a6) will increase coverage by 0.01%.
The diff coverage is 0.00%.

📣 This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

@@             Coverage Diff              @@
##                2.x    #7346      +/-   ##
============================================
+ Coverage     70.37%   70.38%   +0.01%     
+ Complexity    59731    59728       -3     
============================================
  Files          4850     4850              
  Lines        287193   287212      +19     
  Branches      41727    41728       +1     
============================================
+ Hits         202104   202147      +43     
+ Misses        68177    68147      -30     
- Partials      16912    16918       +6     

Impacted Files	Coverage Δ
...ava/org/opensearch/transport/TransportService.java	78.68% <0.00%> (-1.83%)	⬇️

... and 499 files with indirect coverage changes