Listen for post_save on EmailAsUsernameProxyUser

Before, we were listening to the `allauth.user_signed_up` signed up
signal to create the UserMetadata. This doesn't work if the `User` is
created with the `createsuperuser` management command, as
composed-configuration overrides that to create a user of type
`EmailAsUsernameProxyUser` (which is a subclass of `User`).

dandiapi/api/signals.py

@@ -1,4 +1,4 @@
-from allauth.account.signals import user_signed_up
+from composed_configuration._allauth_support.management.commands import createsuperuser
 from corsheaders.signals import check_request_enabled
 from django.conf import settings
 from django.db.models.signals import post_save
@@ -14,18 +14,16 @@ def cors_allow_anyone_read_only(*, sender, request, **kwargs):
     return request.method in ('GET', 'HEAD', 'OPTIONS')
 
 
-@receiver(post_save, sender=settings.AUTH_USER_MODEL, dispatch_uid='create_auth_token')
-def create_auth_token(*, sender, instance=None, created=False, **kwargs):
-    """Create an auth token for every new user."""
+# TODO: remove this receiver if https://github.com/girder/django-composed-configuration/issues/187
+# is fixed
+@receiver(post_save, sender=createsuperuser.user_model, dispatch_uid='initialize_new_user')
+@receiver(post_save, sender=settings.AUTH_USER_MODEL, dispatch_uid='initialize_new_user')
+def initialize_new_user(sender, instance, created=False, **kwargs):
+    """Create an auth token and `UserMetadata` for every new user."""
     if created:
         Token.objects.create(user=instance)
-
-
-@receiver(user_signed_up)
-def user_signed_up_listener(*, sender, user, **kwargs):
-    """Create UserMetadata whenever a user signs up."""
     if settings.AUTO_APPROVE_USERS:
         status = UserMetadata.Status.APPROVED
     else:
         status = UserMetadata.Status.INCOMPLETE
-    UserMetadata.objects.get_or_create(user=user, status=status)
+    UserMetadata.objects.get_or_create(user=instance, defaults={'status': status})