Add configuration for custom block sized index inputs

[kotwanikunal]

Description

• Adds in a node level configuration node.searchable_snapshot.block.size to enable block size tuning at node level for searchable snapshots
• The configuration raises an exception if the block size is not defined as a power of 2 which is an internal constraint for the block manipulation logic

Issues Resolved

Resolves #6480

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)

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/12618/
• CommitID: 70335af
  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/12619/
• CommitID: 3b94229
  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:

      1 org.opensearch.indices.replication.SegmentReplicationRelocationIT.testPrimaryRelocationWithSegRepFailure
      1 org.opensearch.indices.replication.SegmentReplicationAllocationIT.testSingleIndexShardAllocation

• URL: https://build.ci.opensearch.org/job/gradle-check/12620/
• CommitID: 38a4da4
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[kotwanikunal]

Whitesource failure fix is addressed by #6629

[andrross]

Does this still work as expected if there are existing blocks on disk and then the node is restarted with a different block size setting?

[kotwanikunal]

Does this still work as expected if there are existing blocks on disk and then the node is restarted with a different block size setting?

That will cause issues when recovering the cache at node boot. I was planning to wrap the exception and link to the API from #6030 .

[kotwanikunal]

Changing the block size value for the node will lead to undesirable circumstances since we do not have a mechanism currently to migrate the existing blocks to the new block size.
We will need some persistent config through which we can figure out when the value is changed, and perform a migration or clear out the file cache.
Owing to the shortcomings as well as the nature of the config (used only for tuning), this feature will not be a part of the GA release for searchable snapshots.
This will be re-visited when we have these decisions ironed out.

#6480 (comment)

Closing out the PR in the meanwhile.