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

GRPCClient is an implementation of WrapperPluginClient service that talks over RPC.

GRPCServer is the gRPC server that GRPCClient talks to.

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

this is the interface for the plugin service NOTE there are 2 versions - the server interface (implemented by the actual plugin) - the client interface (implemented by the client stub) this is because the signature of the client and server are difference when using grpc streaming.