Change pinned timestamp file format stored in remote store

[sachinpkale]

Description

• As part of Add timestamp pinning service and scheduler to update in-memory state #15180, we introduced a way to pin/unpin timestamp and stored the end state in the configured remote store.
• But storing all the pinned timestamps in a file can have concurrency issues even if we create immutable files to store the info.
• While debugging, reading these pinned timestamp files in remote is also not always possible if the content is encrypted.
• To tackle these problems, in this PR, we change the way to store pinned timestamp data. Instead of storing all the timestamps in one file, we create separate, empty file per <timestamp, pinning entity> tuple.
• We name the file as <pinning entity>__<timestamp> which makes debugging easier just by listing the files.

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 7a05214: 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 5c4dcf9: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 28.57143% with 45 lines in your changes missing coverage. Please review.

Project coverage is 71.90%. Comparing base (738cdd3) to head (38c36b9).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...remotestore/RemoteStorePinnedTimestampService.java	25.00%	43 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main   #15526   +/-   ##
=========================================
  Coverage     71.89%   71.90%           
- Complexity    63791    63832   +41     
=========================================
  Files          5249     5247    -2     
  Lines        298149   298109   -40     
  Branches      43084    43084           
=========================================
- Hits         214368   214354   -14     
- Misses        66126    66199   +73     
+ Partials      17655    17556   -99     

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[github-actions]

❌ Gradle check result for bbda09f: FAILURE

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[github-actions]

❌ Gradle check result for 18569c8: FAILURE

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[github-actions]

❌ Gradle check result for 18569c8: 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 38c36b9: UNSTABLE

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

[sachinpkale]

Changes are mostly covered in the integ tests. CodeCov is failing as it does not consider coverage from integ tests.