Dead letters commands customer settings

[net-free]

https://github.com/cloudblue/django-cqrs/pull/39#issuecomment-971441722

Hey,

I've found that this Pull Request is breaking cqrs_dead_letters retry command.

_get_consumer_settings used to return 2 arguments and with this change it start to return tuple of 3, which is breaking init_broker method in above mentioned command. Exact line:

queue_name, dead_letter_queue_name = RabbitMQTransportService.get_consumer_settings()

is raising ValueError: too many values to unpack (expected 2)

[net-free]

duplicate #49