VDR: For a SubjectID it should be possible to create a new DID after deactivation

[stevenvegt]

If we want users to provide a subjectID so they can map it to their internal customer administration, a deactivation of a subject should not be permanent.
Currently it is not possible to recreate a DID for a subject with a disabled DID:

level=warning msg="CreateSubject failed" error="could not store DID documents: subject already exists" module=VDR operation=CreateSubject operationID=CreateSubject requestURI=/internal/vdr/v2/subject user="<nil>"

[reinkrul]

We could create DIDs for methods with no active DIDs for the particular subject. Would also provide a (manual) upgrade path for when we add a new DID method.