docker/windows: build rust image in the ci

docker/windows: build rust image in the ci

This makes it a bit harder to build an image locally with the script,
as now the rust image requires to pass it the base image tag as a
--build-arg. This way though we don't need to duplicate and keep
the string of the image in sync.

Another thing is that now the docker windows image build is properly
passing/replacing build args and we can build non-master versions
of the image too.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-ci/-/merge_requests/405>