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

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,
and aims to become the canonical registry in the future. It is however
currently configured to be a partial mirror of registry.fd.o, where
only the most-downloaded container images can be found.

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 0bd9a062e1ab ("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: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7913
Acked-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Signed-off-by: Martin Roukala (né Peres) <martin.roukala@mupuf.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20450>