[Backport] [2.x] [Streaming Indexing] Enhance RestClient with a new streaming API support (#14437)

[reta]

Backport of #14437 to 2.x

[github-actions]

❌ Gradle check result for 2b1ea3e: FAILURE

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[github-actions]

❌ Gradle check result for b4034b9: FAILURE

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[github-actions]

❌ Gradle check result for b4034b9: FAILURE

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[github-actions]

❌ Gradle check result for d7a5e20: FAILURE

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[github-actions]

❌ Gradle check result for c4d9324: FAILURE

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[github-actions]

❌ Gradle check result for a5323d3: FAILURE

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[github-actions]

✅ Gradle check result for 191daa0: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 18.99038% with 337 lines in your changes missing coverage. Please review.

Project coverage is 71.39%. Comparing base (e5e1bad) to head (191daa0).
Report is 32 commits behind head on 2.x.

Files	Patch %	Lines
...rc/main/java/org/opensearch/client/RestClient.java	31.70%	83 Missing and 1 partial ⚠️
...va/org/opensearch/client/ReactiveDataProducer.java	0.00%	63 Missing ⚠️
...va/org/opensearch/client/ReactiveDataConsumer.java	0.00%	53 Missing ⚠️
...org/opensearch/client/ReactiveRequestProducer.java	0.00%	49 Missing ⚠️
.../rest/action/document/RestBulkStreamingAction.java	0.00%	23 Missing ⚠️
.../java/org/opensearch/client/StreamingResponse.java	0.00%	17 Missing ⚠️
...rg/opensearch/client/ReactiveResponseConsumer.java	0.00%	15 Missing ⚠️
...n/java/org/opensearch/client/StreamingRequest.java	43.47%	12 Missing and 1 partial ⚠️
...c/main/java/org/opensearch/client/Cancellable.java	0.00%	7 Missing ⚠️
...t/src/main/java/org/opensearch/client/Message.java	0.00%	7 Missing ⚠️
... and 4 more

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #15089      +/-   ##
============================================
- Coverage     71.48%   71.39%   -0.10%     
- Complexity    62677    62705      +28     
============================================
  Files          5123     5135      +12     
  Lines        294480   295009     +529     
  Branches      42912    42972      +60     
============================================
+ Hits         210518   210618     +100     
- Misses        66286    66714     +428     
- Partials      17676    17677       +1     

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[reta]

@andrross this is a backport for streaming Rest Client for 2.x: the large difference is that 2.x is still uses Apache HttpClient 4.x, more things needed to be implemented there (hence the difference in files), thank you!