turn environment config into toml files

[ctheune]

Should be a relatively simple replacement and will help embedding structured config more easily and would get rid of most type conversion issues.

Long term we want this to be different anyway, but this is a low hanging next step.

• automatic migration step .cfg -> .toml
• how does this interact with secrets / embedded secrets?

[elikoga]

Do we want this to completely replace the old configparser/configupdater format, so automatic migration step .cfg -> .toml is part of a ./batou migrate?

Also: What updating library to use?

In python 3.11 there is https://docs.python.org/3/library/tomllib.html, but there also is https://github.com/python-poetry/tomlkit with more support