Auto-generate CLI and config docs from code

[Johennes]

We currently manually maintain the documentation of CLI flags and config options under docs/. For CLI flags we're additionally duplicating this information in the code (see e.g. https://github.com/jhugman/uniffi-bindgen-react-native/blob/main/crates/ubrn_cli/src/ios.rs#L116) so that clap can use it. It would be great if we could organize this data in one place. Preferably it would be the code because then we cannot forget to update the docs after changing the code.

Options we could consider for generating docs from the code include https://github.com/ConnorGray/clap-markdown or maybe even just cargo doc with some light script processing.