[steer_bot_hardware_gazebo] Implement POSITION_PID and VELOCITY_PID like default_robot_hw_sim.cpp

[nyxrobotics]

Thanks for the great work, this repository is very nice to run steering robots on gazebo.

I would like to see PID modes added to the steering position controls and wheel speed controls.
ODE has a problem with vibrating and slipping if PID is not used to control the joint.

In gazebo_ros_control is the following part
https://github.com/ros-controls/gazebo_ros_control/blob/46f41d0b8b90e4b29c2500123d879e768bba830c/src/default_robot_hw_sim.cpp#L201-L216

If you all agree, I will develop this feature and create a PR.

[MoriKen254]

thank you so much.
could you do it please?