Curvenote --> MyST 🎉

[rowanc1]

This is a major push upstream of functionality that has been developed in curvenote over the last three years.

The major functionality added on this push is around pdf export, latex export, intersphinx support, citation support, docx export, and latex templating.

There are no changes to mystjs package beyond a few improvements of bugs to fix around code highlighting, all files are now living in a single git repo.

The changes have been highlighted here:
executablebooks/meta#838

Directly after merging/testing this PR we will add another pass on docs, and issues for immediate next steps to continue cleaning things up.

[fwkoch]

Running this locally:
✅ npm install and npm run build work
✅ npm run tests passes locally
✅ npm run dev builds and watches myst-cli which functions as expected

Looking at the changes added after moving things over from curvenote, no issues stand out...

[rowanc1]

Ok I am going to merge this in, as this PR is more about moving homes than actually reviewing the code. Future PRs will be smaller than 1900 commits!

That being said, anyone following along please feel free to continuing commenting on this PR if you have specific feedback about a package/file/etc.

There are many, many things that need to be fixed up, and the project is absolutely in beta (especially the CLI). We are aiming to make rapid progress over the coming weeks and months, and are also aiming to move into a more open process as things become more stable.

Please consider this a start in it's new EBP home! 🚀