Note: This is a "RFC", as support for discussion, not a "diff to review", per se.
- extract SWHID model type definition in a dedicated module,
- add support for SWHID on Origin objects using the hexlified url as id,
- refactor RawExtrinsicMetadata to use only SWHID as target and origin fields,
- use a newly defined SWHIDObjectType enum type as SWHID.type field,
- adapt the rest of the code accordingly.