Add flags for RabbitMQ message TTL & queue expiry

Adds two new flags to alter behaviour in RabbitMQ:
    * `rabbitmq_message_ttl_ms`, which lets you set a TTL on messages.
    * `rabbitmq_queue_expiry_ms`, which lets you set an expiry time on queues.
See https://www.rabbitmq.com/ttl.html for more information on both.

Change-Id: I51ca37ffbb1bb5c07f2d39873f0f33ca20263f2a