Add parameter default_planning_scene to load planning scene geometry on startup

[pac48]

Description

This PR adds a new parameter to the move_group node that allows users to specify a planning scene file to load on startup. The parameter is a string containing the absolute file path. The parameter can be set with either $(find-pkg-share pkg-wth-planning-file) for XML or ament_index_python.packages.get_package_share_directory in Python to facilitate specifying the path. If the parameter is not specified, the move_group node will behave as it previously did. If there is an error loading the file, the node will exit with a fatal error.

Checklist

• Extend the tutorials / documentation reference
• Create tests, which fail without this PR reference

[sjahr]

I think this is too dangerous because you're not locking the planning scene when writing to it (see

moveit2/moveit_ros/planning/planning_scene_monitor/include/moveit/planning_scene_monitor/planning_scene_monitor.h

Line 170 in 19d4a28

* @warning Most likely you do not want to call this function

).
You can get thread safe access like this:

{
  planning_scene_monitor::LockedPlanningSceneRW ps = planning_display_->getPlanningSceneRW();
  if (ps)
     FANCY MODIFICATIONS
} // End scope to release lock

[github-actions]

This PR is stale because it has been open for 45 days with no activity. Please tag a maintainer for help on completing this PR, or close it if you think it has become obsolete.

[sjahr]

@pac48 Should we close this?

[pac48]

@sjahr We should try to merge this. I think the change to the test should either be deleted or more effort has to be put in to make it not flaky.