Automate PyPI releases

[kinow]

We can automate the whole process of reviewing the version, that it's a tag, and that it's uploaded to PyPI with existing GitHub Actions used in multiple other projects. Here are some examples that I am aware of or worked with in the past:

• Cylc, https://github.com/cylc/cylc-flow/blob/4aa492d95c82bc55ac2f49b7beeefb057fcae48c/.github/workflows/1_create_release_pr.yml & https://github.com/cylc/cylc-flow/blob/4aa492d95c82bc55ac2f49b7beeefb057fcae48c/.github/workflows/2_auto_publish_release.yml
• RO-Crate-py https://github.com/ResearchObject/ro-crate-py/blob/619ba5e3b6c4fdd687b42d33c1819761d8db4503/.github/workflows/python-publish.yml
• Annif https://github.com/NatLibFi/Annif/blob/8d8603301b860d5793d7d61756c91a0c628db5e9/.github/workflows/cicd.yml#L167-L206

[kinow]

Note: we must not test this with our official package in PyPI. I believe RO-Crate-py uses the test-pypi instance. It's an old service offered by PyPI so that devs can test that everything works before publishing a release. We can fork it or create a new repo, play with actions, and then once we are confident of how things work, then we schedule half-day to cut the first release (and solve any issues).

Then future releases should take between 30 and 180 seconds, I think (tests are taking 30 seconds at the moment). After this time, the package would then be available on PyPI, with the GitHub tag created, etc.

https://test.pypi.org/