(collision monitor) add limit polygon type (ros-navigation#3519)

* add LIMIT polygon type

* fix unit tests

* Fix MIN_POINT doesn't exist

* Fix Action type enum

* FIX velocity used

* FIX unit test point distance

increase point distance to not be in limit field

* Update collision_monitor_node_test.cpp

* fix status name not updated

* [MOD] only single linear limit

* Apply review comments

* Update nav2_collision_monitor/include/nav2_collision_monitor/types.hpp

---------

Co-authored-by: Steve Macenski <stevenmacenski@gmail.com>

nav2_collision_monitor/README.md

@@ -29,6 +29,7 @@ The following models of safety behaviors are employed by Collision Monitor:
 
 * **Stop model**: Define a zone and a point threshold. If more that `N` obstacle points appear inside this area, stop the robot until the obstacles will disappear.
 * **Slowdown model**: Define a zone around the robot and slow the maximum speed for a `%S` percent, if more than `N` points will appear inside the area.
+* **Limit model**: Define a zone around the robot and clamp the maximum speed below a fixed value, if more than `N` points will appear inside the area.
 * **Approach model**: Using the current robot speed, estimate the time to collision to sensor data. If the time is less than `M` seconds (0.5, 2, 5, etc...), the robot will slow such that it is now at least `M` seconds to collision. The effect here would be to keep the robot always `M` seconds from any collision.
 
 The zones around the robot can take the following shapes: