[Examples] Fix Vicuna serve example and add OpenAI Example for Vicuna

[cblmemo]

This PR adds an OpenAI Compatible Endpoint for Vicuna. It also fixed a version issue in our Vicuna example.

This is required for our SkyServe User Doc; I feel like if we could start from an existing example, it would make the understanding easier.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
  • sky launch those two YAMLs and make sure them works
• Backward compatibility tests: bash tests/backward_comaptibility_tests.sh

[Michaelvll]

Thanks for fixing this @cblmemo! Do we need to update the installation for Vicuna training yaml as well?

[cblmemo]

Thanks for fixing this @cblmemo! Do we need to update the installation for Vicuna training yaml as well?

I'm not super familiar with the training part of the fastchat... Maybe @infwinston could give some insight here?