Feature Request: Save metadata fields into Handle PID records

Overview of the Feature Request
Right now Dataverse supports two PID systems: DOI and Handle. Along with the location and preserver persistent identifier both receives some metadata as well. The DOI metadata is based on the Datacite metadata schema, and it contains several metadata fields, while Handle contains only two fields: HS_ADMIN, and URL. It would be great if - as far as possible - Handle would store the same set of metadata. Although there is an important difference between the two systems: Datacite provides a metadata schema, while Handle does not have a metadata schema, it accepts any list of key-value pairs, so a first iteration should provide an ad hoc key names, that later could be improved either by make the mapping configurable by the Dataverse administrator, or by providing mappings to metadata schemas.

What kind of user is the feature intended for?
(Example users roles: API User, Curator, Depositor, Guest, Superuser, Sysadmin)
I guess this feature would be most useful for the Depositors, whose data will be more interoperable outside of Dataverse.

What inspired the request?
The discussion about FAIR Digital Object concept (see https://fairdo.org/1316-2/) and its implementation within GWDG.

What existing behavior do you want changed?
The metadata field set passed to Handle PID is extended.

Any brand new behavior do you want to add to Dataverse?
No

Any open or closed issues related to this feature request?
No

Are you thinking about creating a pull request for this feature?
Yes.

Start by reviewing Dataverse's existing DOI and Handle PID metadata handling and comparing the metadata currently sent to each system. Define the first-iteration key-value mapping and determine how it should be tested. Done means Handle records preserve the supported metadata fields alongside HS_ADMIN and URL, with tests covering the resulting metadata.