[Backport-2.x] REST API to initialize an extension and dynamically load

[owaiskazi19]

Description

Backport of #8029

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

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: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18141/
• CommitID: e37d6ab
  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: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18142/
• CommitID: a566ce2
  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: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18183/
• CommitID: a566ce2
  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: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18188/
• CommitID: 2cece27
  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:

      2 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString
      1 org.opensearch.remotestore.SegmentReplicationUsingRemoteStoreIT.testDropPrimaryDuringReplication

• URL: https://build.ci.opensearch.org/job/gradle-check/18202/
• CommitID: efd9bd3
  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

Merging #8210 (efd9bd3) into 2.x (efd12df) will decrease coverage by 0.10%.
The diff coverage is 68.27%.

@@             Coverage Diff              @@
##                2.x    #8210      +/-   ##
============================================
- Coverage     70.64%   70.55%   -0.10%     
+ Complexity    56851    56766      -85     
============================================
  Files          4703     4704       +1     
  Lines        269104   269133      +29     
  Branches      39774    39787      +13     
============================================
- Hits         190118   189881     -237     
- Misses        62702    62912     +210     
- Partials      16284    16340      +56     

Impacted Files	Coverage Δ
...c/main/java/org/opensearch/bootstrap/Security.java	33.09% <ø> (+0.23%)	⬆️
.../src/main/java/org/opensearch/env/Environment.java	87.78% <ø> (+0.66%)	⬆️
...rch/extensions/rest/RestActionsRequestHandler.java	100.00% <ø> (ø)
...rch/extensions/rest/RestSendToExtensionAction.java	46.66% <ø> (ø)
.../main/java/org/opensearch/action/ActionModule.java	95.03% <33.33%> (-0.47%)	⬇️
server/src/main/java/org/opensearch/node/Node.java	85.97% <50.00%> (-0.02%)	⬇️
...org/opensearch/extensions/ExtensionDependency.java	66.66% <60.00%> (-7.02%)	⬇️
...a/org/opensearch/extensions/ExtensionsManager.java	43.50% <60.52%> (-13.57%)	⬇️
...extensions/rest/RestInitializeExtensionAction.java	73.01% <73.01%> (ø)
...ain/java/org/opensearch/tasks/CancellableTask.java	80.76% <81.25%> (-6.19%)	⬇️
... and 2 more

... and 468 files with indirect coverage changes