Describe the proposal

Currently, if you do something like:

builder.Services.AddActors(options =>
{
    options.Actors.RegisterActor<MyActor>(nameof(MyActor));
});

The complete interface hierarchy needs to be compatible with actors. So if you have something like:

public interface IInternalMyActor : IMyActor
{
    void SomeInternalMethod()
}

public interface IMyActor: IActor
{
    Task SomeMethod()
}

public class MyActor: Actor, IInternalMyActor{
   // TODO: implementation
}

If you try to start this actor host you will get the following error message:

: 'Method 'SomeInternalMethod' of actor interface 'MySample.IInternalMyActor ' does not return Task or Task<>. The actor interface methods must be async and must return either Task or Task<>. (Parameter 'actorInterfaceType')'

Error happens at InterfaceDescription:224.

It would be nice if we would be able to provide at the actor registration another generic parameter which interface should be used to access the actor. So like:

builder.Services.AddActors(options =>
{
    options.Actors.RegisterActor<IMyActor, MyActor>(nameof(MyActor));
});

That would make it possible to have a quite complicated structure of interface on an actor. Also it would make it alot easier to use default interface methods, because you can have an more advanced IActor interface in your project that just map members from the class Actor, so you can use it in your default interface methods.