add ros<->highlevel command server

[k-okada]

ros_server_udp.cpp subscribes high_state and send to realrobot, and publishes robot status to high_cmd

The document (https://github.com/unitreerobotics/unitree_ros_to_real#run-the-package) said lcm_server do same job, but I think it just convert UDP packet to LCM packet and have nothing to do with ROS

https://github.com/unitreerobotics/unitree_legged_sdk/blob/f3b318a691e744e28caf6787eec90288f4016e87/include/unitree_legged_sdk/lcm_server.h#L94-L99

(and moreover, it needs

// need to keep original cmd.head to move robots
    std::array<uint8_t, 2> head = cmd.head;
    cmd = ToLcm(SendHighROS, cmd);
    cmd.head = head;

to control robot via UDP.