Migrate from setup.py to Poetry pyproject.toml for packaging and environment management

[d33bs]

This PR migrates from a setup.py file to a Poetry-flavor pyproject.toml file for packaging and environment management of this project. I've also added a pre-commit check which ensures the pyproject.toml file and poetry.lock file are in good form for possible changes as things grow with this package.

As part of this effort I also added https://github.com/rhysd/actionlint, https://github.com/tox-dev/pyproject-fmt, https://github.com/python-poetry/poetry (poetry-check) pre-commit checks to help ensure the work is well prepared and keeps consistent over time.

Thanks for any feedback you may have!

Depends on and should be merged after #55
Addresses the first step of #52

[falquaddoomi]

Really glad to see the project moving over to Poetry! I made a few comments to do with version pinning and the OpenAI API key, but otherwise this looks great.

[d33bs]

Thank you @miltondp and @falquaddoomi for your reviews! Merging this in now.