Feature request: Pluggable actor factories

[jasonvasquez]

Describe the proposal

I would like to be able to inject dependencies into my Actor instances as they are activated. Right now, it appears that the ActorManager's createActor function only allows instantiating the class directly. At time of registration, it would be ideal if I could provide an (optional) factory function that could instantiate the class and then hand it back to Dapr to continue. Alternatively, perhaps the runtime could accept a subclass of ActorManager that could extend it to provide custom factory functions.