Support removing model version parent
Refs https://redmine.teklia.com/issues/5452
An API user with admin access on the model should be able to remove the parent from a model version by setting parent=None in (Partial)UpdateModelVersion
Refs https://redmine.teklia.com/issues/5452
An API user with admin access on the model should be able to remove the parent from a model version by setting parent=None in (Partial)UpdateModelVersion