ci: have mergify set the component/build label on PRs
ci: have mergify set the component/build label on PRs

Quite a few PRs have the `build:` prefix. It would be good to teach
Mergify to set the label for those.

Signed-off-by: Niels de Vos <7bda0c0ee7f47171cc808e9e60292cbc5d8140dd@redhat.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi