[Documentation]Check that you cannot delete a subscription: If the subscription id provided does not correspond to any existing subscription in the system then an error of type ResourceNotFound shall be raised
[Documentation]Check that you cannot retrieve a subscription: If the identifier provided does not correspond to any existing subscription in the system then an error of type ResourceNotFound shall be raised
[Documentation]Check that you cannot update a subscription: If the NGSI-LD System does not know about the target Subscription, because there is no existing Subscription whose id (URI) is equivalent, an error of type ResourceNotFound shall be raised