GCP authentication with GCS, key file required

[thibaultserti]

I'm using imgproxy on GCP in a GKE cluster with workload identity enabled. Therefore, I don't need any key to authenticate.
The way it is designed here renders it required and so I have no way to not specify a key.

https://github.com/imgproxy/imgproxy-helm/blob/master/imgproxy/templates/env-secret.yaml#L330=

In fact it is really ambiguous here because the doc says it should work without:
https://docs.imgproxy.net/serving_files_from_google_cloud_storage?id=setup-credentials