[WIP] Add e2e test for `tune` api with LLM hyperparameter optimization

[helenxie-bit]

What this PR does / why we need it: This PR adds an e2e test for the tune API, specifically for the scenario of importing external models and datasets for LLM hyperparameter optimization.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Checklist:

• [ ] Docs included if any changes are user facing