[ROS2] Move head / wheelchair_collision planning scene update to ada_planning_scene.py

[amalnanavati]

As discussed in #142 and documented in an in-code TODO , we should move the logic to move the planning scene’s head and wheelchair collision objects from the MoveToMouth tree to ada_planning_scene.py. Only foreseeable issue with that is too frequently updates of the parameter scene while face detection is on, so we could consider adding a parameter to specify the rate at which to send the latest update (based on a detected face) to MoveIt.