[rag evals][2/n] add more braintrust scoring fns for RAG eval

[yanxi0830]

What does this PR do?

• add more braintrust scoring functions for RAG eval
• add tests for evaluating against context

Test Plan

pytest -v -s -m braintrust_scoring_together_inference scoring/test_scoring.py

Example Output

• https://gist.github.com/yanxi0830/2acf3b8b3e8132fda2a48b1f0a49711b

Sources

Please link relevant resources if necessary.

Before submitting

• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [ ] Ran pre-commit to handle lint / formatting issues.
• [ ] Read the contributor guideline, Pull Request section?
• [ ] Updated relevant documentation.
• [ ] Wrote necessary unit or integration tests.