Add occupancy flattening node (converts to costmap) #642

Job	Run time
Setup Environment	24s
Build/Test (action, behaviour_planning)	1m 1s
Build/Test (action, global_planning)	1m 1s
Build/Test (action, local_planning)	50s
Build/Test (action, model_predictive_control)	2m 13s
Build/Test (infrastructure, foxglove)	1m 21s
Build/Test (interfacing, can_interfacing)	50s
Build/Test (interfacing, sensor_interfacing)	1m 1s
Build/Test (infrastructure, data_stream)	49s
Build/Test (perception, depth_estimation)	51s
Build/Test (perception, lidar_object_detection)	59s
Build/Test (perception, radar_object_detection)	54s
Build/Test (perception, tracking)	53s
Build/Test (samples, cpp_aggregator)	53s
Build/Test (samples, py_producer)	48s
Build/Test (samples, py_transformer)	1m 3s
Build/Test (world_modeling, hd_map)	1m 2s
Build/Test (world_modeling, motion_forecasting)	49s
Build/Test (world_modeling, occupancy)	1m 25s
Build/Test (world_modeling, occupancy_segmentation)	1m 27s
Build/Test (world_modeling, localization)	51s
Confirm Build and Unit Tests Completed	0s
	21m 25s

Provide feedback