metadata: add copyrights

[kpsherva]

• closes migration: copyright and license CERNDocumentServer/cds-rdm#381
• proposal of the solution to add copyrights field, discussed on the 8th of April telecon
• I tried to apply what we came up with in the breakout room and:
  • I explored the possibility of adding the field alongside license field. Unfortunately the current implementation of license field is a bit too rigid to handle this, license field would need to be refactored (unfortunately this is not feasible in the scope of this PR)
  • putting the field inside the modal requires some thoughts and design on the UX of representing the current value when updating the record
  • explored adding the value to datacite serializer, it seems we don't have a field to accommodate it at the moment https://datacite-metadata-schema.readthedocs.io/en/4.5/properties/rights/

[tmorrell]

For the DataCite serialization, you can add it to rightsList with structure:

{
      "rights": "Put text from the copyright field here",
      "rightsUri": "http://rightsstatements.org/vocab/InC/1.0/"
 }

[tmorrell]

"copyright" seems like a better label to me. My main argument is that since it's a single text field (not a list) the singular makes more sense. This is probably a bit of a US vs EU thing too (I've never used "copyrights" as a term).

I'll also raise a minor point about the length restriction. Could it be one character in case someone just wanted to use the copyright symbol?

[kpsherva]

done, thank you for the suggestions!

[tmorrell]

Looks good! Looks like it might need black run.