XD-1629/1653 RabbitMessageBus Enhancements

- Add retry options (back off etc)
- Add Recoverer so failed messages can be routed to a DLQ
- Add prefix to queues/exhanges for configuring HA/DLE via policy

XD-1629 Polishing; Mapped Headers

- add commented props to servers.yml
- add support for mapped headers, with default map all