build napari-docs on theme PR

[psobolewskiPhD]

Add a GitHub workflow to build the current napari docs (dev) using a PR branch of this theme. Note at the moment I'm letting the gallery build, but deleting the .doctrees folder which was 400Mb!

This partially addresses https://github.com/napari/napari-sphinx-theme/issues/155 The CircleCI previews would be more user friendly, but require some extra secrets.

[psobolewskiPhD]

You can see for example the mastodon link from previous PR: https://github.com/napari/napari-sphinx-theme/pull/153

[psobolewskiPhD]

Dang, nuking the .doctrees saved 500Mb. the artifacts listed as <100 mb and unzipped it's <130 locally:

❯ du -h -d 1
832K    ./_downloads
296K    ./roadmaps
5.4M    ./_modules
2.1M    ./plugins
7.2M    ./gallery
2.5M    ./_sources
 18M    ./_static
236K    ./further-resources
3.2M    ./release
 63M    ./_images
724K    ./_tags
1.3M    ./guides
6.1M    ./api
4.6M    ./tutorials
 52K    ./_sphinx_design_static
600K    ./community
8.4M    ./howtos
1.1M    ./naps
1.9M    ./developers
129M    .

[psobolewskiPhD]

As an alternative we could build just the mini-site that is in this repo, but it has few of the napari.org features. You can see that here: https://github.com/psobolewskiPhD/napari-sphinx-theme/pull/1

[jni]

Fantastic, thanks! 🚀