Create Project Auth Method

Adds a sign-in method. apple, google and firebase derive their issuer (firebase from firebase_project_id). An oidc issuer must be https and serve an OpenID Connect discovery document that declares the same issuer and a jwks_uri; a provider that fails that check is a 400. A project accepts one method per issuer, and one email method: a second is a 409. An email method's link_domain must be a web paywall domain of one of the project's applications, or it is a 400. A 403 means Superwall Auth is not available to the project yet. Requires projects:write scope.