Make (at least) the zipCode a required field in provider-registration

[benbender]

At the moment, only the name is required to register a provider. If you do so, the mediator can't verify this provider as the backend expects the zipCode to be provided and throws an (invisible) error.

Imho: At least the name and a complete address should be necessary to register a provider to lower the friction in daily operations (even if technically it may not be needed).