Multiverse Actors

[jspenger]

The Portals Actor Runtime currently only runs on a single workflow. It would be a good idea to extend this with abstractions to run the runtimes on different workflows. Such that actors on different workflows/runtimes can message each other. This would enable developing exactly-once actor runtimes, one for each microservice/universe. The open tasks are to add abstractions for sending messages across different actor universes, and routing the messages accordingly. In addition to this, there should be an option to connect two actor runtimes that are running in different Portals deployments. It is probably a good idea to, at the same time, explore the addition of virtual actors in this mode.