add external properties to SolutionInfo

This interface can be customized by the user to state when/where additional execution hooks should run.

Author: v4hn

msgs/msg/SolutionInfo.msg

@@ -12,3 +12,7 @@ uint32 stage_id
 
 # markers, e.g. providing additional hints or illustrating failure
 visualization_msgs/Marker[] markers
+
+# user-defined values that can provide additional information,
+# e.g., whether to switch a suction gripper on or off or when to call some other execution interface
+Property[] external