Add E-Mail address registration to login flows

Try to add the regsitration of a missing e-mail address into the SAML/OIDC login flows.

Most services need a valid e-mail address and the regsitration of such is outside of the login flow. If a user logs in for a SP/RP, the login fails, because of the missing e-mail. The regsitration of such an address is then handled, but the login flow is broken. The user has to call the initial SP/RP again, instead of just continuing.