Our HTML assets aren't being served compressed because our Google Cloud
Storage bucket doesn't know that compressing them is okay.

We use the `-z` option (patched with
https://github.com/GoogleCloudPlatform/gsutil/pull/1430 via
gitlab-org/gitlab-build-images!472)
to tell Google that certain files can be uploaded compressed. See
https://cloud.google.com/storage/docs/gsutil/commands/cp for more
details.

Relates to
https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/14852