Use `x-dead-letter-routing-key` argument

[brianstorti]

Instead of binding the dlx queue to the same routing key as the working queue, we bind it to the value of the argument x-dead-letter-routing-key to avoid sending the rejected message to multiple queues.

Example:

1) Queues a and b are bound to routing key x, in the same exchange; 2) A message is received and consumed successfully by queue a, but queue b rejects it; 3) The handler would publish the message to the dead-letter exchange using the routing key x, causing it to end up in both dead-letter queues (a.dlx and b.dlx).

With this change, as long as these two queues where declared with a different x-dead-letter-routing-key, the message would end up just in the queue that originally rejected it.

We would probably use the queue name as the x-dead-letter-routing-key value to guarantee uniqueness.

[jjbohn]

:+1:

[toreriklinnerud]

@brianstorti should we merge?

[brianstorti]

I'll merge it tomorrow morning. Still need to add this new argument in the workers that are using the gem, shouldn't take more than 10 minutes.