Bugfix in snapshot V2 restore flow

[sachinpkale]

Description

• If snapshot is created between last fetch of pinned timestamps and index deletion and last metadata file is created before the last fetch, the restore of snapshot will restore data corresponding to previous snapshot
• Consider following set of events:

09:58 - second last metadata file
10:00 - S1
10:30 - last metadata file
10:55 - last refresh of pinned timestamp
11:00 - S2
11:05 - Index deleted

• Here, restoring S2 will restore data corresponding to snapshot S1.
• In this PR, we make sure to not delete latest metadata file if pinned timestamps are enabled.
• When the last snapshot that has reference to the deleted index gets deleted, the remote data will be cleaned up.

Related Issues

• [BUG] [Snapshot V2] Restore of latest snapshot post index deletion can restore data only till previous snapshot #16339

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 b89a761: 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 678c225: FAILURE

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[github-actions]

✅ Gradle check result for 261428a: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.98%. Comparing base (35c366d) to head (261428a).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...index/translog/RemoteFsTimestampAwareTranslog.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16332      +/-   ##
============================================
- Coverage     72.10%   71.98%   -0.13%     
+ Complexity    64862    64793      -69     
============================================
  Files          5307     5307              
  Lines        302606   302612       +6     
  Branches      43717    43719       +2     
============================================
- Hits         218208   217827     -381     
- Misses        66541    66939     +398     
+ Partials      17857    17846      -11     

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