feat: added ResponseRelevanceEvaluator

[poshinchen]

Description

1. Add ResponseRelevanceEvaluator to assess the relevance of the LLM response to the question, in other words, how focused the LLM response is on the given question.
2. Implement 5-level scoring system (Not At All, Not Generally, Neutral/Mixed, Generally Yes, Completely Yes)

Related Issues

#100

Documentation PR

WIP

Type of Change

1. New feature ("ResponseRelevance Evaulator")

Notes

• Need to run evaluations via agentcore online evaluator and compare the scores.

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[poshinchen]

There are some duplicated extraction logic comparing with other evaluators. The follow-up will be to extract them in a better place. Currently Evaluator base class is not the best option because it contains non trace-based evaluators implementation. This is not a blocker though.