Allow to generate manifest (TOML) from project directory

[hoijui]

Given a project repository (local checkout),
we would generate an okh.toml manifest file,
with as much data as we manage to gather automatically.
The remaining fields may be:

1. omitted,
2. added with placeholder values
   (like "TODO" or "https://TODO.com/YOUR_ORG/YOUR_REPO/")
3. same as 2., but commented out

Previous issue: https://gitlab.com/OSEGermany/osh-tool/-/issues/4

NOTE:

• Use projvar to gather lots of the required info
• Use this suggestion
  to figure out [[part]]s of the project