Add command handler interface with no events

[lucabriguglia]

I'm going to add a new command handler interface with the handle method that does not return any events:

public interface ICommandHandlerAsync<in TCommand> where TCommand : ICommand
{
    Task HandleAsync(TCommand command);
}

Looking for a name suggestion as ICommandHandlerAsync is already used for the existing one that has events.

[lucabriguglia]

Not needed any more, a command handler can now return an empty command response