adding tests for all the agent runners

[dhrubo-os]

Description

[adding tests for all the agent runners + refactoring the necessary code for the agent runners]

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Attention: 89 lines in your changes are missing coverage. Please review.

Comparison is base (94c5d21) 82.69% compared to head (c1d0c6b) 82.91%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
.../ml/engine/algorithms/agent/MLChatAgentRunner.java	90.25%	17 Missing and 18 partials ⚠️
.../ml/engine/algorithms/agent/MLFlowAgentRunner.java	86.40%	9 Missing and 8 partials ⚠️
...ch/ml/engine/algorithms/agent/MLAgentExecutor.java	90.26%	3 Missing and 8 partials ⚠️
...org/opensearch/ml/common/MLCommonsClassLoader.java	18.18%	8 Missing and 1 partial ⚠️
...nsearch/ml/engine/algorithms/agent/AgentUtils.java	92.13%	4 Missing and 3 partials ⚠️
...va/org/opensearch/ml/common/utils/StringUtils.java	0.00%	6 Missing ⚠️
...rithms/metrics_correlation/MetricsCorrelation.java	33.33%	2 Missing ⚠️
...c/main/java/org/opensearch/ml/engine/MLEngine.java	50.00%	1 Missing ⚠️
...rch/ml/engine/algorithms/agent/PromptTemplate.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1783      +/-   ##
============================================
+ Coverage     82.69%   82.91%   +0.22%     
- Complexity     4744     4869     +125     
============================================
  Files           462      467       +5     
  Lines         18940    19674     +734     
  Branches       1976     2060      +84     
============================================
+ Hits          15662    16313     +651     
- Misses         2451     2500      +49     
- Partials        827      861      +34     

Flag	Coverage Δ
ml-commons	82.91% <88.22%> (+0.22%)	⬆️

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[joshuali925]

this should be something like

        if (!clusterService.state().metadata().hasIndex(ML_AGENT_INDEX)) {
            listener.onFailure(new ResourceNotFoundException("Agent index not found"));
        }

it's not returning a response when index is not found

[ylwu-amzn]

Thanks Joshua. @jngz-es help fix this part?

[jngz-es]

sure, will fix it in my pr.

[ylwu-amzn]

Fixed in #1866