Add a one-time queue size command.

[software-opal]

We're trying to integrate monitoring of the queue size into Icinga and it would be really helpful if there was a way to output only one iteration of the monitor command.

[tsteur]

👍 be really helpful indeed. would it only need one number for one specific queue?

[software-opal]

I was just thinking the current command, but instead of running in a while 1 loop; exiting after the first print.