[Suggestion] Subscribe to non-empty queue event #19

There should be a privileged command that allows a user to monitor a queue. Mostly intended for slow moving queues where if a queue becomes non-empty everyone that subscribed to that queue gets a DM saying there are people waiting in the queue.

For my use there's no need for any other events than when the queue moves from being empty to contain at least 1 user, so I won't advocate for other events.

The current alternative is to check the queue periodically, which isn't ideal. Potential abuse is covered by the existing /blacklist command, and silently dropping DMs (as a kind of cooldown) would break the principle of least surprise.