Add error handling for plan&execute agent

[Hailong-am]

Description

1. Remove line separator from tool's response
2. Index mapping tool support raw input for index parameter
3. Add json extract logic for LLM output is not json format

Related Issues

#3848

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[pyek-bot]

Thanks for the fixes @Hailong-am ! Let me know when it is ready for review. Can you also please create an issue for the fixes involved in this PR? Thanks!

[Hailong-am]

Thanks for the fixes @Hailong-am ! Let me know when it is ready for review. Can you also please create an issue for the fixes involved in this PR? Thanks!

@pyek-bot PR description updated with issue number and the what's the actual fix, please help to take a look

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 77.99%. Comparing base (c3b1fd6) to head (3f00b45).

Files with missing lines	Patch %	Lines
...thms/agent/MLPlanExecuteAndReflectAgentRunner.java	0.00%	2 Missing ⚠️
...g/opensearch/ml/engine/tools/IndexMappingTool.java	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3845      +/-   ##
============================================
+ Coverage     77.98%   77.99%   +0.01%     
- Complexity     7316     7320       +4     
============================================
  Files           655      655              
  Lines         33037    33043       +6     
  Branches       3708     3709       +1     
============================================
+ Hits          25764    25773       +9     
+ Misses         5688     5684       -4     
- Partials       1585     1586       +1     

Flag	Coverage Δ
ml-commons	77.99% <50.00%> (+0.01%)	⬆️

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[pyek-bot]

Thanks for the fixes! Looks good!