symfony/scheduler support

[kbond]

I don't believe this bundle will support symfony/scheduler messages out of the box. This is because the SendMessageToTransportsEvent isn't fired when dispatching scheduled messages.

I think what we'd need to do to support is:

1. WorkerMessageReceivedEvent: if scheduled message:
   • create/persist StoredMessage with $dispatchedAt === $receivedAt
   • add MonitorIdStamp here
2. WorkerMessageHandledEvent: update as normal