A preparation to introduce HTTP server ([[ https://linear.app/comm/issue/ENG-3520/blob-service-scaffold-http-server | ENG-3520 ]]).
Renamed `--port` CLI option to `--grpc-port` and added another `--http-port` option. Both gRPC and HTTP servers will be able to run concurrently.
Also changed the type to `u16` to make it compatible with actix-web API I'm going to use.
Depends on D7440