Add Obstacle Costmap Plugin Layer

1. Adds a rectangular costmap window of a configurable size as an obstacle of LETHAL_OBSTACLE cost (254).
2. The plugin can be added to the nav2 params file in the local and/or global costmap params as follows:

  add_obstacle_layer:
    plugin: nav2_costmap_2d::AddObstacleLayer
    enabled: True
    update_window_height_m: 1.5
    update_window_width_m: 0.5

3. The obstacles are published as a geometry_msgs/msg/Point message on the "/summit/sensor_obstacles" in the map frame.

ros2 topic pub /summit/sensor_obstacles geometry_msgs/msg/Point "x: 1.0
y: -4.5
z: 0.0"

4. For having the plugin enabled we have to checkout the humble-costmap-update branch of this navigation2 repo and then build and source only the nav2_costmap_2dpackage if the navigation2 is installed via apt.

colcon build --symlink-install --packages-select nav2_costmap_2d
. install/setup.bash

5. Plugin inspired from Keepout Filter and Gradient Layer plugin.
6. Add Obstacle Layer implementation can be found here: header file and source file.