Set up default currency accounts automatically (#72)

backend/product/payments/service.go

@@ -206,7 +206,7 @@ func (s *Service) Fetch(ctx context.Context, a *customer.Account) (Snapshot, err
 	if err := s.ready(); err != nil {
 		return Snapshot{}, err
 	}
-	subject, err := s.Identity.Subject(ctx, a)
+	subject, err := s.ensureAccounts(ctx, a)
 	if err != nil {
 		return Snapshot{}, err
 	}