DOCS: adding/updating a list of external frontends (and extensions)

[chrishavlin]

Based on discussion in #4822 I think it'd be great to add a list of external frontends to the docs somewhere to increase their visibility. Also, it looks like it's time to update https://yt-project.org/extensions.html

In terms of externally packaged frontends, I know of the following:

• yt_aspect, loads ASPECT and general .pvtu files, maintained by myself.
• idefix (the topic of ENH: support installing yt_idefix as pip install yt[idefix]; plug it in docs #4822), maintained by @neutrinoceros

In terms of the https://yt-project.org/extensions.html page, I'd propose the following:

• replace yt interaction and ViewYT with yt_idv
• add entry for yt_napari

If you know of any others (frontends or extensions), if you add them here in the comments and I'll include them in a PR (or you can add them via your own PR if you want). I'll ping the slack and mailing list to solicit more...

[chrishavlin]

https://libyt.readthedocs.io/en/latest/ should be added to extensions too

[chrishavlin]

https://github.com/dnarayanan/powderday (https://ui.adsabs.harvard.edu/abs/2021ApJS..252...12N/abstract) : maybe not an "extension" per se, but it relies on yt for its infrastructure so I'd like to include a link somehow.

[neutrinoceros]

We could add a section to promote successful users ;)

[chrishavlin]

This is done! see https://yt-project.org/extensions.html for the updated page.

[neutrinoceros]

Thanks a bunch Chris !