Default to administrative metadata from the token instead of making them required

[fpotier]

Summary

Some properties marked as required for creating Dataset (and probably other Objects) could be made optional in the DTO and default to values from the token.

Example CreateDatasetDto.contactEmail could default to the email property contained in the user's JWT

[bpedersen2]

Hmm, at MLZ we will enforce the contact email to be the useroffice@ on all ingested datasets ( we want to avoid GDPR problems), so at least a configurable overruling should possible then.