Add support to skip pinned timestamp in remote translog garbage collector

[sachinpkale]

Description

• As part of shallow snapshot optimisations, we are introducing timestamp based implicit locking support. This feature will be called Timestamp Pinning in remote backed storage. When a timestamp is pinned, remote store garbage collectors will skip deleting data corresponding to the timestamp.
• Changes to segment store garbage collection are made as part of PR: https://github.com/opensearch-project/OpenSearch/pull/15017
• In this PR, we are making following changes to translog garbage collection:
  • Fetch metadata files in reverse-chronological order
  • Filter out metadata files that match with pinned timestamp and metadata files that are created post successful fetch of pinned timestamp.
  • From the remaining metadata files, read min and max generation and filter out generations by pinned timestamp metadata files.

Related Issues

• https://github.com/opensearch-project/OpenSearch/issues/15064

Check List

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

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