Server: Allow multiple queues for the same observable property

Why? To allow independent streams for the same observable property (e.g. metadata-dependent values).

How?

• PropertyIdentifier_on_subscription(self, metadata) -> None should have the return type Optional[Queue[PropertyType]] so that a subscription can lead to another than the default queue
• update_PropertyIdentifier(self, value: PropertyType) -> None should have a new parameter queue: Queue[PropertyType] to specify the target queue of the value update