GZ to ROS topic bridge

[anikk94]

1. Gazebo simulation (gz sim) can not communicate properly with other ros2 components like rviz and moveit because of missing clock/synchronization data.

This is the warning that shows the problem.

[gazebo-5] [WARN] [1737862214.636185121] [controller_manager]: No clock received, using time argument instead! Check 
your node's clock configuration (use_sim_time parameter) and if a valid clock source is available

Added ros to gz topic bridge node as per gazebo documentation.

2. One more change to xarm_controller to fix build failure caused by ros2control upstream change. Missing reference causes build failure. Reference removed based on similar action taken by this clearpath robotics package as seen here: https://github.com/clearpathrobotics/clearpath_robot/pull/115/commits/4a51281617088bb483bd9bc911d4e88cd49943f7