Add QUEUECLEAR command

[mvrhov]

right now you have to list all the jobs in one queue and call DELJOB for each of them to celar jobs on one queue. This is cumbersome and takes a lot of time if there is a lot of jobs.

[antirez]

That's true. However Disque is a cluster so such a command should work in a way to make the queue deletion cluster-wide, at least if an additional option is specified (or omitted). Like:

DELQUEUE myqueue LOCAL # Only local queue deletion

DELQUEUE myqueue # Broadcast of a DELQUEUE message to all the reachable nodes

However such command would not be as resistant to failures as explicitly acknowledging all the jobs in a queue will be: in that case if nodes with a copy are unreachable, we'll wait to complete the GC.