[Backport 3.3] combine json chunks from requests

[opensearch-trigger-bot]

Backport 305cb8e from #4317

[codecov]

Codecov Report

❌ Patch coverage is 19.23077% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.08%. Comparing base (592a193) to head (2e704fb).
⚠️ Report is 2 commits behind head on 3.3.

Files with missing lines	Patch %	Lines
.../opensearch/ml/rest/RestMLExecuteStreamAction.java	19.23%	21 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3    #4349      +/-   ##
============================================
- Coverage     80.11%   80.08%   -0.03%     
- Complexity    10171    10200      +29     
============================================
  Files           855      855              
  Lines         44238    44373     +135     
  Branches       5113     5135      +22     
============================================
+ Hits          35441    35537      +96     
- Misses         6646     6671      +25     
- Partials       2151     2165      +14     

Flag	Coverage Δ
ml-commons	80.08% <19.23%> (-0.03%)	⬇️

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