[Snapshot V2] Fix for create snapshot build and test failures

[anshu1106]

Description

This is followup for #15124.

1. This PR fixes :server:japicmp failure found during 2.x backport of the above PR.

2. With existing delimiter :, integ test fails with following error:
   https://build.ci.opensearch.org/job/gradle-check/46330/testReport/junit/org.opensearch.remotestore/RemoteRestoreSnapshotIT/testCreateSnapshotV2WithRedIndex/
   In this PR, we are changing the delimiter from : to __

Related Issues

Resolves #15123

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for e773ee1: 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 e773ee1: FAILURE

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[github-actions]

❌ Gradle check result for 1936f24: FAILURE

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[github-actions]

❌ Gradle check result for 67a41c2: FAILURE

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[github-actions]

❌ Gradle check result for 462d62d: FAILURE

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[github-actions]

✅ Gradle check result for e380db2: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 71.84%. Comparing base (33be5a9) to head (9d2eb9b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...in/java/org/opensearch/snapshots/SnapshotInfo.java	0.00%	4 Missing ⚠️
.../org/opensearch/repositories/FilterRepository.java	0.00%	2 Missing ⚠️
...ch/repositories/blobstore/BlobStoreRepository.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #15602      +/-   ##
============================================
- Coverage     71.99%   71.84%   -0.15%     
+ Complexity    63924    63870      -54     
============================================
  Files          5257     5257              
  Lines        298667   298675       +8     
  Branches      43184    43184              
============================================
- Hits         215028   214593     -435     
- Misses        65972    66453     +481     
+ Partials      17667    17629      -38     

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[github-actions]

❌ Gradle check result for 4fc5ed0: 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 9d2eb9b: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.snapshots.DedicatedClusterSnapshotRestoreIT.testSnapshotWithStuckNode
      1 org.opensearch.action.admin.cluster.node.tasks.ResourceAwareTasksTests.testTaskResourceTrackingDuringTaskCancellation

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