Handshake is a common handshake that is shared by plugin and host.

PluginMap is a ma of the plugins supported, _without the implementation_ this used to create a GRPC client.

GRPCClient is an implementation of PluginManager service that talks over GRPC.

GRPCServer is the gRPC server that GRPCClient talks to.

PluginManagerPlugin is the implementation of plugin.GRPCServer so we can serve/consume this.

PluginManager is the interface for the plugin manager service.