Add PyPI release job

[alexfikl]

This mostly uses the tutorial from here https://packaging.python.org/en/latest/guides/publishing-package-distribution-releases-using-github-actions-ci-cd-workflows/

To work for actual releases, it needs:

• A pypi environment on Github: https://docs.github.com/en/actions/managing-workflow-runs-and-deployments/managing-deployments/managing-environments-for-deployment
• Adding the Github repo as a "trusted publisher" on PyPI: https://docs.pypi.org/trusted-publishers/adding-a-publisher/

I think we can add a step here to also make a Github release at the same time, but that would require a bit of scripting to get the changelog from CHANGELOG.md. Should be doable though.

@alejandrogallo @jghauser

[alexfikl]

This also adds a step to make a Github release now:

• The release is named Version v0.14.
• It contains the info from the latest release from CHANGELOG.md.
• It also uploads the wheel and sdist, in case anybody wants them from here instead of from PyPI

[alexfikl]

All of this is a bit experimental, so we might need to do a few 0.14rc releases to make sure it all works as expected!