CI: Publish workflow (PyPI)

[danielhollas]

This adds a GHA workflow for publishing to PyPI.

This uses the relatively new Trusted Publisher authentication mechanism, which does not require storing a secret token in repository settings (we should consider migrating aiida-core to this as well imo).

The workflow itself is triggered when a tag is created (Typically by creating a release on GitHub UI). Additionally, one can test the release by publishing to TestPyPI by adding a test-release label to a PR.

I have used this workflow in another (non-AiiDA) repository and it's been working well.

Closes #72

[danielhollas]

I don't think the __version__ attribute is very useful for this package and it complicates package management so I am removing it. Dissenters will be pointed to a lengthy discussion thread on CPython forum full of people arguing about this. :-D

[unkcpz]

Please point me to the lengthy discussion, would be a nice read material after dinner.

[danielhollas]

🤣

https://discuss.python.org/t/brainstorming-eliminating-dynamic-metadata/71405

Here you go. :-)

[danielhollas]

I decided to first publish a version 0.0.1 which should be fully backwards compatible and can be used by existing users.

[danielhollas]

@unkcpz @agoscinski can you take a look? Once I have a green light on this workflow I'll add instructions for maintainers into docs.

[danielhollas]

@unkcpz @agoscinski Also can you please send me your user names on PyPI so that I can add you as maintainers of the aiida-test-cache package? Let me know if other people should be added. Thanks!