Metadata requests

[MarkGotham]

Metadata requests from @magiraud for the YAML files:

• Priority: data already included in the paths -- make explicit separate fields for
  • opus name/number, movement name/number (blank if not relevant)
  • lyricist name
• Also easy and perhaps useful: (first) time/key signature (extracted from score as currently implemented in When in Rome)
• Possibly also: (approx.) year of composition (would need to extract/retrieve first).

https://gitlab.com/algomus.fr/dezrann/dezrann-corpus/-/issues/42#note_1117014924