docs: RAG evaluation notebook using traces (#1857)

* evaluate_rag notebook

* final thoughts

* style fix

* cleanup

* remove unnecessary data file

* fix spelling

* Update tutorials/evals/evaluate_rag.ipynb

Co-authored-by: Xander Song <axiomofjoy@gmail.com>

* Update tutorials/evals/evaluate_rag.ipynb

Co-authored-by: Xander Song <axiomofjoy@gmail.com>

* Update tutorials/evals/evaluate_rag.ipynb

Co-authored-by: Xander Song <axiomofjoy@gmail.com>

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Co-authored-by: Xander Song <axiomofjoy@gmail.com>