Fix publish documentation or migrate to a new service

[josecsotomorales]

Documentation is not being pushed to:

https://sqlalchemy-continuum.readthedocs.io/en/latest/

We should look at fixing this or replacing it with something like GitHub Pages instead.

[marksteward]

I'm in favour of GitHub pages, readthedocs is another thing to go wrong

[josecsotomorales]

Will migrate existing docs to GitHub Pages and build a CI/CD pipeline to automate publishing 🚀