[Backport 2.x] hidden model implementation

[opensearch-trigger-bot]

Backport d71c77f from #1736

[codecov]

Codecov Report

Attention: 51 lines in your changes are missing coverage. Please review.

Comparison is base (16e2cdf) 81.31% compared to head (14179d5) 82.05%.

Files	Patch %	Lines
...h/ml/action/deploy/TransportDeployModelAction.java	68.60%	19 Missing and 8 partials ⚠️
.../java/org/opensearch/ml/utils/RestActionUtils.java	65.21%	6 Missing and 2 partials ⚠️
...h/ml/action/models/DeleteModelTransportAction.java	75.86%	0 Missing and 7 partials ⚠️
...arch/ml/action/models/GetModelTransportAction.java	87.50%	1 Missing and 2 partials ⚠️
...n/java/org/opensearch/ml/model/MLModelManager.java	81.25%	0 Missing and 3 partials ⚠️
...ain/java/org/opensearch/ml/common/CommonValue.java	0.00%	1 Missing ⚠️
...ansport/upload_chunk/MLRegisterModelMetaInput.java	92.85%	0 Missing and 1 partial ⚠️
...action/undeploy/TransportUndeployModelsAction.java	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #1755      +/-   ##
============================================
+ Coverage     81.31%   82.05%   +0.73%     
- Complexity     4372     4430      +58     
============================================
  Files           425      425              
  Lines         17478    17605     +127     
  Branches       1849     1870      +21     
============================================
+ Hits          14213    14445     +232     
+ Misses         2539     2419     -120     
- Partials        726      741      +15     

Flag	Coverage Δ
ml-commons	82.05% <80.97%> (+0.73%)	⬆️

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