Auto boot actors on system startup

[rogeralsing]

An often requested feature is the ability to boot specific actors during system start. e.g. say you want all your PlayerActors to boot up before getting any direct messages.

I'm thinking this ought to be super easy to set up. e.g. plugin that just reads a list of actor names from a DB. then send a Touch message to each of them. (just loop over a stream from the DB, we don't even need to read them all into memory.)

[rogeralsing]

https://github.com/asynkron/protoactor-dotnet/blob/dd8e7983951037a95edbee8ca443e83cc885b1b9/src/Proto.Cluster/Singleton/SingletonManager.cs

[rogeralsing]

Very much related to https://github.com/asynkron/protoactor-dotnet/issues/1114