[WIP] Multiple queues

[Nyholm]

I want to implement the possibility to use multiple queues/backends. This PR is not ready for merge.

   tags: 
      - { name: fervo_deferred_event.listener, event: first, method: onFirst, backend: default }
      - { name: fervo_deferred_event.listener, event: second, method: onSecond, backend: otherBackend }

I've made sure that you may configure the bundle for multiple backends. I followed the pattern from SwiftMailerBundle.

I got some problem I want some help solving.

Service configuration

There is a lot of services depending on the backend configuration.

• fervo_deferred_event.queue.sidekiq
• fervo_deferred_event.queue.amqp
• fervo_deferred_event.service.message_service

Should we duplicate these for each backend? Like:

• fervo_deferred_event.defaut.queue.sidekiq
• fervo_deferred_event.otherBackend.queue.amqp
• etc

The listener

Should we create a duplicate for fervo_deferred_event.listener for each backend as well?

Same event different backends

How do we solve the problem when the same event should be deferred to multiple backends?
Look at these lines

   tags: 
      - { name: fervo_deferred_event.listener, event: first, method: onFirst, backend: default }
...
   tags: 
      - { name: fervo_deferred_event.listener, event: first, method: onFirst, backend: otherBackend }