Add a community notebook for fine-tuning with QLoRA, PEFT, and MLflow

[daniellok-db]

What does this PR do?

This PR adds a community notebook tutorial for fine-tuning an open-source LLM using QLoRA and PEFT, using MLflow for experiment tracking.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
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  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

cc @stevhliu as the recommended reviewer for documentation

[LysandreJik]

Thanks @daniellok-db!