Traefik also serves an internal entrypoint that all addon services
(bridges, bots, etc.) depend on, so it makes sense to have it be
available early on. It is injected as a systemd `required` dependency
for all services, so it would have been pulled earlier anyway (despite
the priority). Nevertheless, it's better to make the playbook-defined
priotities for services match, so that services are explicitly asked to
start in a more correct order.

With these changes in place now, all "start service" tasks executed by
Ansible cause a "change", indicating that all these services are started
in the correct order and none of them is unintentionally started as a
dependency for another.