Cloud Build FAST CI/CD workflow needs Docker pull by default

[ludoo]

The CB workflow in FAST uses the alpine:3 image by default, which won't work when the Docker registry is not reachable. We should mention this in docs and a workflow comment, and potentially add a remote artifact registry in the IaC project when Source Repo / Cloud Build CI/CD is enabled.

[ludoo]

Reopen, as I associated to the wrong PR.