Automate releases

[jtpio]

With #798 now in place, we are one step away from automating releasing.

The missing step is to upload the wheel and sdist to PyPI, and the @voila-dashboards/jupyterlab-preview extension to npm (if it has changed).

Linking to some resources for reference and inspiration:

• https://github.com/vaexio/vaex/blob/master/.github/workflows/wheel.yml
• https://github.com/vaexio/vaex/blob/master/.github/workflows/wheel-universal.yml

cc @maartenbreddels who is also interested in this

[jtpio]

We will probably want to use https://github.com/jupyter-server/jupyter_releaser directly once it's out of the experimental phase.

[jtpio]

Closing as fixed.

v0.2.13 was just released with the Jupyter Releaser: https://github.com/voila-dashboards/voila/releases/tag/v0.2.13