[Backport] [2.3] Compatibility issue with /_mget: RHLC 2.x connected to OpenSearch Cluster 1.x (#4812)

[reta]

Backport of #4812 to 2.3

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/5245/
• CommitID: ada2b11

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/5261/
• CommitID: 7635456

[codecov-commenter]

Codecov Report

Merging #4876 (7635456) into 2.3 (4dd4c1f) will increase coverage by 0.12%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##                2.3    #4876      +/-   ##
============================================
+ Coverage     70.58%   70.70%   +0.12%     
- Complexity    57122    57207      +85     
============================================
  Files          4585     4585              
  Lines        274514   274516       +2     
  Branches      40229    40230       +1     
============================================
+ Hits         193762   194106     +344     
+ Misses        64539    64147     -392     
- Partials      16213    16263      +50     

Impacted Files	Coverage Δ
...va/org/opensearch/action/get/MultiGetResponse.java	70.32% <50.00%> (-0.46%)	⬇️
...g/opensearch/index/analysis/CharFilterFactory.java	0.00% <0.00%> (-100.00%)	⬇️
...a/org/opensearch/tasks/TaskCancelledException.java	50.00% <0.00%> (-50.00%)	⬇️
...cluster/coordination/PendingClusterStateStats.java	20.00% <0.00%> (-48.00%)	⬇️
...arch/search/aggregations/pipeline/LinearModel.java	23.07% <0.00%> (-46.16%)	⬇️
...ons/bucket/terms/ParsedSignificantStringTerms.java	33.33% <0.00%> (-42.86%)	⬇️
...cluster/coordination/PublishClusterStateStats.java	33.33% <0.00%> (-37.51%)	⬇️
...pensearch/action/ingest/DeletePipelineRequest.java	31.25% <0.00%> (-37.50%)	⬇️
...opensearch/snapshots/SnapshotMissingException.java	28.57% <0.00%> (-28.58%)	⬇️
...rc/main/java/org/opensearch/ingest/IngestInfo.java	51.72% <0.00%> (-27.59%)	⬇️
... and 480 more

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