fix(docker): fix compose race conditions on mariadb_init

We want the dependent services to wait until the initialization service
of mariadb finishes, but also properly accept if it already exited
before a leaf service gets picked up and put into created state. By
using the service_completed_successfully signal, we can ensure precisely
this, without being racy and leading to none booted services.

While at it, remove the compose version identifiers as docker-compose
deprecated them and always warned about when running docker-compose.