Publish packages to PyPI

[dokterbob]

1. Create initial release of packages
2. Document release engineering process in RELENG.md
3. Consider automating release process:

Open question: should all versions be in sync and publication happen everywhere simultaneously?
Or separate releases?

The latter is more in line with the fact that our packages are independent. But might be harder to implement, practically.

Resources:

• https://pypi.org/project/hatch-semver/
• https://hatch.pypa.io/latest/version/#updating
• https://github.com/azu/monorepo-github-releases
• https://www.amarjanica.com/automate-github-releases-with-release-please/
• https://trunkbaseddevelopment.com/
• https://www.reddit.com/r/devops/comments/1ebi0e2/how_are_you_guys_dealing_with_github_monorepo/