Automated documentation generation using `mkdocs` and GitHub Actions

[sujaypatil96]

Automated documentation generation in this repo should be pretty straightforward since we have only one script (etl.py) and we've been pretty good about maintaining the docstrings for the classes and methods that we've defined/used in that script.

We should do another pass of reviewing those docstrings and making sure they're still accurate (method signature, description, etc.).

Once that's done, we can use the mkdocs framework like we do in a lot of our other repositories to have a public-facing website capturing documentation relevant to the repository. We can use mkdocs plugins/mkdocstrings to first appropriately format, and then automatically parse out documentation sections into web pages, and have them be rendered using mkdocs and deployed to GitHub Pages.

All of these processes should be automated using GitHub Actions.