Add MathJax plugin

[fish-not-phish]

Is it possible to officially add the MathJax plugin to this project?

I have forked the repo and my implementation works, but it would be nice if it was a part of this repository as well so I can continue to get any of the fantastic updates from the contributing authors here.

I could see a lot of folks that might benefit from adding this plugin :)

My fork is here:
https://github.com/fish-not-phish/django-ckeditor-5