Refactor CLI API

[xiaoyu-work]

Describe your changes

1. CLI - APIs now shares a unified entrypoint. Any future CLI can be easily added as an API.
2. Remove duplicated olive.run from cli api file.
3. Add a real integ test to test file.

Checklist before requesting a review

• Add unit tests for this change.
• Make sure all tests can pass.
• Update documents if necessary.
• Lint and apply fixes to your code by running lintrunner -a
• Is this a user-facing change? If yes, give a description of this change to be included in the release notes.
• Is this PR including examples changes? If yes, please remember to update example documentation in a follow-up PR.

(Optional) Issue link

[shaahji]

session_params_tuning.py also needs to be updated to return the workflow output.

[xiaoyu-work]

/azp run

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