auth operation not integrated

[qiuzhong]

It seems the auth operation is not intergrated with the bridge as rosauth.js is never required or referred by the bridge implementation. The authentication function is implemented, though.

[minggangw]

The rosauth should act as a service in ROS, and ros2-web-bridge has to call the rosauth service when ['op'] == 'auth'. In ROS2, there has not been defined such a srv as ROS1 does, we better pend this requirement.