Manage python requirements in a pyproject.toml file

[rlskoeser]

This update should replace top-level requirements.txt and all the text files under requirements/ folder.

It may be helpful to refer to this packaging guideline https://learn.scientific-python.org/development/guides/packaging-simple/ and the official pyproject documentation https://packaging.python.org/en/latest/guides/writing-pyproject-toml/

Here's an example pyproject.toml file from one of our other CDH django projects: https://github.com/Princeton-CDH/mep-django/blob/main/pyproject.toml

You will have to update the github actions python installation for this change.