Registration form should be built with the information provided by the backend

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Is your feature request related to a problem? Please describe.
The form shown in the registration URL (/register) is hard-coded in the Register component.

Describe the solution you'd like
Plone backend has a way to say which fields should be available in the registration form. The point here is to call that endpoint in the /register route and build the form dynamically with the backend information.

Describe alternatives you've considered
None.

Additional context
We have done this in the past with the user information form. See #2917