DLQ (dead letter queue) support

[ryanwitt]

qdone's builtin failed queues are nice, but if a job repeatedly fails, it can be useful to get a developers attention on it by sending it to a master failed queue after some number (say 3 or 5) attempts. Furthermore, it may be an advantage to have dynamically named DLQs so this allows for that as well.

Add an option --dlq-name NAME and --dlq-after 5 to activate DLQ support on failed queues.

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In SureDone, there are several scenarios where this is potential problem currently:

• channel imports trigger creation of dynamic user based product level import queues
  • those jobs fail for some reason, and never are caught as the failed queues do not send to dead letter queues
• bulk jobs still mysteriously don't complete sometimes
  • bulk jobs are put on user based dynamically created user based queues and failures are invisible without dlq
• critical sold action inventory update queues are put on dynamically created user based queues
  • we currently have no visibility into if/when these processes fail without dlq