Verify if per-authenticator config of default registration form works

As reported by user:

Once I set the form in the federation settings (and removed them in the
facility settings), the registration button started showing up.

I guess the general setting will be overridden with 'empty' if you don't
set anything on the federation/idp level.
From a user perspective that's a bit unexpected / unintuitive.
When setting the form for the facility I get this in the config:
unity.saml.requester.registrationFormForUnknown=SSORegistration
but NO mention of
unity.saml.requester.metadataSource.UPSTREAM.perMetadataRegistrationForm

When setting the form on the federation level I get this in the config:
unity.saml.requester.metadataSource.UPSTREAM.perMetadataRegistrationForm=SSORegistration

This makes me wonder when the general setting is ever applied or how the
override mechanism works.
If, in effect, the registration form setting in the facility is always
overridden then that dropdown could be removed from the config form to
reduce confusion.