Improve Release Engineering

[bollwyvl]

Challenge

As we hope to land more features, we'd like to see the robustness of cutting releases improve.

Proposal

• From Support JupyterLab 3 (and 2?) #27 (comment), we have some agreement on an initial path forward to improving our ability to confidently build and ship release artifacts.

GitHub action on release creation event.

Yeah, I feel like this is usually not worth the automation. I'm a big fan, however, of doing a single CI build of release artifacts, and only testing against them, rather than in-tree code, and making them available in a single release bundle. Then moving it up to github, pip, npm, whatever, isn't really that hard, as these things are good at handling tarballs :P