Switch to mkdocs material theme for documentation

[browniebroke]

Description

Explore replacing our theme by mkdocs-material.

Light theme:

Dark theme:

Some things I'm not happy about:

• I think the colors for the dark theme aren't quite there yet (especially the contrast of the links).
• Syntax highlighting for code snippets is lost unless we switch to code fences (no idea how it works now) figured it out and ported the exiting solution to limit the diff
• This theme has a lot of features, there might be more to enable

Syntax highlighting

Existing solution relies on prettify-1.0.js which is apprently coming from https://github.com/googlearchive/code-prettify

• JS is added to the main HTML document
• There is a piece in theme.js which adds the class prettyprint to all <pre> tags
• The main HTML doc run prettyPrint() on load (via the onload HTML attribute). This function finds all elements with the class above and add syntax highliting to them

I've replicated this in mkdocs-material, however there is some client side navigation, which means we need to listen to another event than DOM content loaded. This is explained in their docs

[browniebroke]

Configured a dummy RTD project to have a live deployment of the PR: https://browniebroke-drf--2.org.readthedocs.build/en/2/