[Segment Replication] Update bwc test to rely on segments for verification

[dreamer-89]

Description

This change improves the testIndexingWithSegRep bwc test by relying on _cat/segments API to verify shard store and doc count and is preferred because of below reasons:

1. index/_stats API does not return data for all shards specially when it is newly created (this is probably not all shard copy have documents and thus no stats), thus test fails as mentioned here [Backport] [Segment Replication] Added mixed and rolling upgrade bwc test (#7537) #7626 (comment)
2. The only reason for _stats was to build nodeId to shardId map so that targeted _search can be made using "_shards:" + shardNumber + "|_only_nodes:" + nodeId preference. This is unnecessary two step process.
3. _cat/segments resonates better with segment replication as we are verifying segment names and doc count.

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)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18392/
• CommitID: a2fea06
  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.cluster.allocation.ClusterRerouteIT.testDelayWithALargeAmountOfShards
      1 org.opensearch.action.admin.indices.create.CreateIndexIT.testCreateAndDeleteIndexConcurrently
      1 org.opensearch.action.admin.indices.create.CreateIndexIT.classMethod

• URL: https://build.ci.opensearch.org/job/gradle-check/18403/
• CommitID: 4de7ebc
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #8267 (e57f170) into main (4c02dd1) will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #8267      +/-   ##
============================================
+ Coverage     70.90%   70.92%   +0.02%     
- Complexity    56710    56764      +54     
============================================
  Files          4733     4733              
  Lines        268333   268333              
  Branches      39322    39322              
============================================
+ Hits         190254   190325      +71     
+ Misses        61996    61986      -10     
+ Partials      16083    16022      -61     

see 451 files with indirect coverage changes

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18536/
• CommitID: 88af9e9
  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.snapshots.RestoreSnapshotIT.testRestoreInSameRemoteStoreEnabledIndex
      1 org.opensearch.remotestore.SegmentReplicationUsingRemoteStoreIT.testNodeDropWithOngoingReplication

• URL: https://build.ci.opensearch.org/job/gradle-check/18537/
• CommitID: e57f170
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[dreamer-89]

@kotwanikunal : Request for review