Adds Sphinx config to generate Python SDK docs.

[dom96]

Usage:

# set up venv with sphinx and sphinx-markdown-builder installed
make markdown

This will generate something like https://gist.github.com/dom96/4ce2594239d4672262eefed992402563.

[danlapid]

I don’t have any strong or smart opinions on how to generate docs for this.
I’ll delegate to @hoodmane to review this 🙏

[hoodmane]

sphinx-markdown-builder doesn't look super well maintained but it gets some commits. It would be nice if we could generate html directly and use that, but it wouldn't look like the rest of the cloudflare docs. I'm interested to see if this looks okay when rendered. Anyways, if we start out with this approach and find something else we like better later then we can just change it.