Patron Registration

This will create a new patron, by the given identifier.

This will redirect the user to the chosen identity provider, for signup.

This will redirect the user to the chosen identity provider, and create the user in the LMS. [See a sequence flow diagram](https://storage.googleapis.com/open-library-api-files/images/idp.png).

This will tell if it is possible to register a new patron, using the given identifier.

This will tell if it is possible to register a new patron, using the given identifier. The patron can then be registered through `POST /patron/registration/identifier`.