[Helm] Support the GKE Workload Identity

[chrisduong]

It had been mentioned here https://discuss.airbyte.io/t/logging-to-gcs-with-workload-identity-in-airbyte-on-gke/6731

In the security point of view, we should use the GKE Workload Identity instead. This means we don't need to set global.storage.gcs.credentialsJson.

However it is not possible, as the Helm chart always requires it.

The remedy is to update the Helm chart to allow global.storage.gcs.credentialsJson to be empty.

[NAjustin]

It's worth noting that there's already a (very stale) issue here for this:
#13081

I agree this would be the ideal solution though when deploying on GKE.