Enhancement: Add support for a mapping for Public Domain Mark url to identifier

[richardhallett]

Add a mapping from rightsURI "https://creativecommons.org/publicdomain/mark/1.0/" to a identifier of "CC-PDM-1.0"

There exists some metadata which does not have an identifier but does list a rightsURI for a public domain work, it would be useful to help identify public domain works by mapping to an identifier.

We use the SPDFX licenst list original source: https://github.com/spdx/license-list-data/blob/master/json/licenses.json
To do our mappings, but they have discussed and decided not to add the public domain work at this time, see spdx/license-list-XML#988

We could extend our own license list (or add a datacite specific one) to add something like:

{
      "reference": "",
      "isDeprecatedLicenseId": false,
      "detailsUrl": "https://wiki.creativecommons.org/wiki/PDM_FAQ",
      "referenceNumber": "",
      "name": "Public Domain Mark 1.0",
      "licenseId": "CC-PDM-1.0",
      "seeAlso": [
        "https://creativecommons.org/publicdomain/mark/1.0/"
      ],
      "isOsiApproved": false
    },

this could help the work of the open access badge in parsec. See https://docs.google.com/document/d/12ZtsSy6PqwYILcJ0FKMLWIOt6xmS9Og6ZiYZzImMicE/edit#