Fix django templates error when getting static files from Google Cloud Storage bucket

[bartacc]

django-storages by default always generates a signed url for downloading data from cloud storage bucket. That's why it threw an error when trying to get static files for /admin route. The solution is to tell django-storages that default ACL is "publicRead" (since the static files bucket is public), because we don't need to use a signed url. File upload is not affected by this change (upload worked correctly before and still works).

For more context you can read this issue on django-storages repo and the part about GS_DEFAULT_ACL variable from the django-storages docs.