Added multiple consumer queues provider support

Currently multiple consumer queues can be configured only statically in the bundle configuration. We have a use case, where specific queues can't be hard-coded (as they are being created dynamically by different agents). So, we need multiple consumer to be able to get a dynamic list of queues. In order to implement this, a queues provider can be used. It should implement a simple interface which returns array of queues (in the same format as used in configuration). The multiple consumer just merges the dynamic queues (if any) with statically configured queues, which are now optional. There is also a check in place to see if at least one of `queues` or `queues_provider` is configured.