CI-Job to publish release versions (tags) to PyPI

Only skipped through this: https://medium.com/maisonsdumonde/gitlab-ci-cd-and-gitlab-pypi-repository-4916a51d22eb

but if the process can be automated, that would be really useful (and we'd reuse it).

Open questions:

• are wheels platform bound? (Do we need to run this on multiple architectures / OS to provide proper packages?)
• command when not using setup.py? is it compatible with both setup.cfg and pyproject.toml?
• can we filter to run this only for the tags with specific form (vX.x.x) ?
• how to check whether the version has been adjusted in project metadata files prior to executing?

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Woooo! Celebration, issue #100 !!!