feat: restrict login to axelerant.com domain

This partially fixes #15 except that we can't remove the code in ct_user yet. That code is responsible for activating the user. We can't enable activation for all registrations as Drupal's user registration form is still enabled. Social Auth module has no feature to enable users created through Social Auth flow.

config/sync/social_auth_google.settings.yml

@@ -2,4 +2,4 @@ client_id: env
 client_secret: env
 scopes: ''
 endpoints: ''
-restricted_domain: ''
+restricted_domain: axelerant.com