For "wizard" style interactive tools it's very annoying if they are
interrupted by kernel log output or PID1's status output. let's add some
infra to disable this temporarily. I decided to implement this as an IPC
service so that we can make this robust: if the client request the
muting dies we can automatically unmute again.
This is hence a tiny varlink service, but it can also be started
directly from the cmdline.
