Support `CITATION.cff`

[ChristianTackeGSI]

Is your feature request related to a problem? Please describe.
No problem.

Describe the solution you'd like
We should look into converting codemeta to CFF and have a proper one in our repo.

See: https://www.hifis.net/spotlights/cff

Describe alternatives you've considered
Just don't support it yet.

Additional context
We might need to support this at some point.
This is basically a note for ourself to re-check on what to do.