Add maths rendering options

[fcooper8472]

We currently use rehype-katex for maths rendering.

It would be great if we could control options either at the section or course level (or both) using the markdown frontmatter.

The katex options are here:
https://katex.org/docs/options.html

So I would imagine something in the markdown for a section like:

katexDisplayMode: true

that would propagate through to toggle the katex displayMode option.

The other important option would be to allow custom macros, e.g. a katex macro specification like this:

macros: {
  "\\dd": "\\frac{{\\mathrm{d}#1}}{{\\mathrm{d}#2}}"
}

Again, ideally, by specifying these macros either in the section or course level.

I'm a little out of my depth, and can't look at this in the next week, but @martinjrobins has pointed me to:

gutenberg/lib/material.ts

for section and course types

and to

gutenberg/components/content/Content.tsx

for where the rehype plugin is used.