cluster-components: Invert the alertmanager alert routing logic

As only the alert matching a specific namespace are routed to the irc-relay today, sending them to the irc relay is acceptable. We need to remove this constraint to be able to receive global cluster alerts like the one relative to the cluster status. If the contraint is remove the irc relay is spammed with the Watchdog alert. The logic need to be inverted to send all the alerts we only want to the irc-relay

Related to swh/infra/sysadm-environment#5036 and swh/infra/sysadm-environment#5281 (closed)