Improve error message for misconfigured connection

If there's no encrypted router the previous error message stated
"missing auto_encryption_opts" which is correct but not helpful.

Also fix printing of database connection alias.

We could potentially go a step further and say "Check your router
config!"

Author: aclark4life

django_mongodb_backend/schema.py

@@ -468,8 +468,9 @@ def _create_collection(self, model):
             auto_encryption_opts = getattr(client._options, "auto_encryption_opts", None)
             if not auto_encryption_opts:
                 raise ImproperlyConfigured(
-                    f"Encrypted fields found but DATABASES['{self.connection.alias}']['OPTIONS'] "
-                    "is missing auto_encryption_opts."
+                    "Encrypted fields found, but `auto_encryption_opts` "
+                    "setting not found in `OPTIONS` setting for "
+                    f"'{self.connection.alias}' database connection."
                 )
             encrypted_fields = self._get_encrypted_fields(model)
             db.create_collection(db_table, encryptedFields=encrypted_fields)