Clarify service registration and deployments

[hpehl]

I think we need to consider how services are added. If multiple applications are deployed, only the first deployment started registers its services with the gRPC server. I'm not sure if there is some variant of a mutable server, but if not, it will take some thought on how this could be done. I don't think we want to stop and restart a server for every deployment being processed. It's experimental, but we might need something like this https://grpc.github.io/grpc-java/javadoc/io/grpc/util/MutableHandlerRegistry.html.

Another thing to consider along these lines is if there are any possible security issues around registering services from different deployments on the same gRPC server. Again, I'd need to read more here to understand how this works. However, we don't want to allow deploymentA to see services from deploymentB.