Add a parameter of the pr-gate-build-job template to specify a
container image URL. If the value is not '' (default), then the
jobs will be run inside a container based on that image.
Signed-off-by: Oliver Steffen <osteffen@redhat.com> Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com> Acked-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Gerd Hoffmann <kraxel@redhat.com> Reviewed-by: Chris Fernald <chfernal@microsoft.com>