Add integration tests for searchable snapshots, Fix length calculation for block based storage

[kotwanikunal]

Description

• Backports Fix length calculation for block based fetching #5055 , Add allocation tests for searchable snapshot remote shards #5048 to 2.4

Issues Resolved

• [Searchable Snapshot] Add integration test for failure scenarios #4962

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: UNSTABLE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/6332/
• CommitID: f7a2991
  Please examine the workflow log, locate, and copy-paste the failure below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/6333/
• CommitID: 5d754bb