[Backport 2.0] Fixing the follower checkpoint updation in follower stats API

[opensearch-trigger-bot]

Backport 6130d6f from #438

[codecov-commenter]

Codecov Report

Merging #440 (c974632) into 2.0 (2243d97) will decrease coverage by 2.30%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##                2.0     #440      +/-   ##
============================================
- Coverage     74.57%   72.26%   -2.31%     
+ Complexity     1001      977      -24     
============================================
  Files           141      141              
  Lines          4562     4565       +3     
  Branches        504      504              
============================================
- Hits           3402     3299     -103     
- Misses          843      943     +100     
- Partials        317      323       +6     

Impacted Files	Coverage Δ
...rch/replication/task/shard/ShardReplicationTask.kt	73.72% <100.00%> (-2.19%)	⬇️
...search/replication/task/shard/TranslogSequencer.kt	86.36% <100.00%> (+0.99%)	⬆️
...cation/action/changes/TransportGetChangesAction.kt	63.49% <0.00%> (-25.40%)	⬇️
...arch/replication/metadata/UpdateMetadataRequest.kt	77.27% <0.00%> (-22.73%)	⬇️
...ch/replication/task/index/IndexReplicationState.kt	51.66% <0.00%> (-15.00%)	⬇️
...ication/action/setup/TransportSetupChecksAction.kt	59.52% <0.00%> (-14.29%)	⬇️
...ication/seqno/RemoteClusterRetentionLeaseHelper.kt	80.00% <0.00%> (-11.67%)	⬇️
...tion/repository/RemoteClusterMultiChunkTransfer.kt	90.24% <0.00%> (-9.76%)	⬇️
.../replication/metadata/store/ReplicationMetadata.kt	62.96% <0.00%> (-8.65%)	⬇️
...action/stop/TransportStopIndexReplicationAction.kt	68.00% <0.00%> (-6.67%)	⬇️
... and 17 more

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