Streamline release process

[Rot127]

We had too many issues with the release process.

• The release build isn't triggered if the release is first saved as draft, then published (https://github.com/orgs/community/discussions/7118).
• The Python wheels get published on any tag, not just on tag + release (see: Only publish if tag is present and workflow is triggered by release. #2766)
• Our release guide for us needs an update.
• More problems I forgot about.

There are also some open questions like:

• Signing tags
• Release naming: Beta1, Beta2 or -rc0, -rc1 ...
• Posting it on social media.