feat: add feature flag for checking allowed data fields

Adds setting for allowed data field check named as:
ENABLE_ALLOWED_DATA_FIELDS_RESTRICTION
The setting defaults False.
When False, app logs a warning message when there is a query
trying to access a field which is not in service's allowed_data_fields

Refs HP-2319

open_city_profile/graphene.py

@@ -208,7 +208,7 @@ def resolve(self, next, root, info, **kwargs):
                     raise FieldNotAllowedError("Field is not allowed for service.")
 
                 logging.warning(
-                    "Allowed data field exception would occur. Field (%s) is not allowed for service %s.",
+                    "Allowed data field exception would occur: Field (%s) is not allowed for service %s.",
                     field_name,
                     info.context.service,
                 )