[Messenger] Use transport agnostic exceptions instead of throwing AMQPException 

**Description**  
If using AMQP, and RabbitMQ is not available, for example, dispatching a message through the bus will throw AMQPExceptions. I think this should be hidden for the client code that uses the bus, since the actual transport may vary.

**Example**  
```php
try {
      $this->messageBus->dispatch((new SampleMessage());
} catch (\AMQPException $e) {
    // Do sth
}``` 