Register GRPC message service

[alpe]

We support the GRPC query handler but there is also a message handler implementation in other modules like:

// RegisterServices registers module services.
func (am AppModule) RegisterServices(cfg module.Configurator) {
	types.RegisterMsgServer(cfg.MsgServer(), keeper.NewMsgServerImpl(am.keeper))
	querier := keeper.Querier{Keeper: am.keeper}
	types.RegisterQueryServer(cfg.QueryServer(), querier)
}

[ethanfrey]

Yeah, that was a new technique that started with rc2 or so.. I think this was defined in ADR 31 or 29?