"CLI" aka a script to run the Inspector (#546)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/546

Not a CLI strictly speaking, but should be good enough for MVP. See Test Plan for how to use it.

Regarding added dependencies:
* pandas: for dataframe usage [here](https://fburl.com/code/5i7nghbq)
* tabulate: for pretty printing [here](https://fburl.com/code/krmppoh8)

***Note***: the changes in "executorch/oss/pyproject.toml" and "executorch/oss/setup.py" are not just for the CLI, but also *necessary* to enable the Python Inspector APIs in OSS.

Reviewed By: tarun292

Differential Revision: D49758493

fbshipit-source-id: 4703ce68a3b2b59c2d50861934434ce5de7f95af