Add CLI dev support, DoenetML interactive

[StevenClontz]

Obsoletes #1959, addresses #2093.

First few commits will create a environment suitable for (some) core PreTeXt development using GitHub Codespaces. In particular, anyone who is comfortable with the https://github.com/PreTeXtBook/pretext-codespace workflow should be able to contribute to our sample documents, and development of PreTeXt XSL can be accomplished similarly. (A future contribution should support full core development support via Codespaces for those who use them, but I'm deferring that to later.)

Then I'll eat the dogfood in the latter case by implementing <interactive platform="doenetml"/> and adding it to the sample article.

[StevenClontz]

See also #2087 which should be massaged in at some point...

[StevenClontz]

woof I wish I had started this a few hours earlier - with all the changes since c195e58d7347a42ad8b1226a781ea04101bd034d for local asset support (a great thing!) I need to wait until a new CLI nightly comes out, or I need to push a new release. Have to table this for at least a few hours anyway...

[StevenClontz]

Then again our nightlies haven't been deploying for a week or so: https://github.com/PreTeXtBook/pretext-cli/actions

Probably need to pair with @oscarlevin to move this forward.