ci/b2c: start making use of the harbor.fd.o

A new container registry was added recently in the fd.o infrastructure. It is located in a datacenter that does not charge for bandwidth usage, but cannot store nearly as much as the Google Cloud Engine can. It is thus configured to be a partial mirror of registry.fd.o, where the only the most-downloaded container images remain.

The address of the new registry is specified in mesa/mesa's CI variables, which means forks will default to registry.fd.o. However, Valve Infra DUTs do not have access to the internet, and instead use another cache proxy hosted locally on the CI gateways. This forced Benjamin to overwrite the registry URL from harbor.freedesktop.org to registry.freedesktop.org in 0bd9a062 ("CI: Overwrite valve infra's registry").

After adding support for the new registry in valve infra, then deploying the update, we are now able to make use of the new container registry. This commit simply rewrites the URL harbor.freedesktop.org into {{ harbor_fdo_registry }}. This variable is set in the valve infra to point to the host:ip of the service, which means changes to the way we deploy this service can be done on the valve-infra side without needing to make changes to every project that makes use of our machines.

Related: #7913 Signed-off-by: Martin Roukala (né Peres) martin.roukala@mupuf.org