Start gz bridge for clock topic (#60)

Start a gz_sim_bridge to have the /clock topic available.

ur_simulation_gz/launch/ur_sim_control.launch.py

@@ -183,6 +183,16 @@ def launch_setup(context, *args, **kwargs):
         condition=UnlessCondition(gazebo_gui),
     )
 
+    # Make the /clock topic available in ROS
+    gz_sim_bridge = Node(
+        package="ros_gz_bridge",
+        executable="parameter_bridge",
+        arguments=[
+            "/clock@rosgraph_msgs/msg/Clock[ignition.msgs.Clock",
+        ],
+        output="screen",
+    )
+
     nodes_to_start = [
         robot_state_publisher_node,
         joint_state_broadcaster_spawner,
@@ -192,6 +202,7 @@ def launch_setup(context, *args, **kwargs):
         gz_spawn_entity,
         gz_launch_description_with_gui,
         gz_launch_description_without_gui,
+        gz_sim_bridge,
     ]
 
     return nodes_to_start

ur_simulation_gz/package.xml

@@ -25,6 +25,7 @@
   <exec_depend>ur_description</exec_depend>
   <exec_depend>ur_moveit_config</exec_depend>
   <exec_depend>urdf</exec_depend>
+  <exec_depend>ros_gz_bridge</exec_depend>
   <exec_depend>ros_gz_sim</exec_depend>
   <exec_depend>xacro</exec_depend>