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

[reta]

Backport of #4812 to 2.x

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/5243/
• CommitID: 23ea00b

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/5257/
• CommitID: 8f1915b

[codecov-commenter]

Codecov Report

Merging #4875 (8f1915b) into 2.x (e53e6ad) will decrease coverage by 0.09%.
The diff coverage is 84.75%.

@@             Coverage Diff              @@
##                2.x    #4875      +/-   ##
============================================
- Coverage     70.69%   70.59%   -0.10%     
- Complexity    57493    57559      +66     
============================================
  Files          4617     4620       +3     
  Lines        276033   276115      +82     
  Branches      40387    40399      +12     
============================================
- Hits         195145   194929     -216     
- Misses        64570    64921     +351     
+ Partials      16318    16265      -53     

Impacted Files	Coverage Δ
...r/routing/allocation/allocator/ShardsBalancer.java	33.33% <33.33%> (ø)
...rch/analysis/common/StemmerTokenFilterFactory.java	7.81% <50.00%> (+1.46%)	⬆️
...va/org/opensearch/action/get/MultiGetResponse.java	70.32% <50.00%> (-0.46%)	⬇️
...org/opensearch/cluster/metadata/IndexMetadata.java	83.31% <62.50%> (-0.33%)	⬇️
.../allocation/allocator/BalancedShardsAllocator.java	90.90% <72.72%> (+3.77%)	⬆️
...ting/allocation/allocator/LocalShardsBalancer.java	85.57% <85.57%> (ø)
...earch/analysis/common/EnglishPluralStemFilter.java	88.13% <88.13%> (ø)
...ster/routing/allocation/AllocationConstraints.java	100.00% <100.00%> (ø)
...pensearch/common/settings/IndexScopedSettings.java	100.00% <100.00%> (ø)
.../main/java/org/opensearch/index/IndexSettings.java	86.64% <100.00%> (+0.07%)	⬆️
... and 494 more

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