Update default recommendation from Obstacles to Cost critic in MPPI (ros-navigation#4170)

Signed-off-by: Steve Macenski <stevenmacenski@gmail.com>

Author: SteveMacenski

nav2_mppi_controller/README.md

@@ -201,7 +201,7 @@ controller_server:
         time_step: 3
       AckermannConstraints:
         min_turning_r: 0.2
-      critics: ["ConstraintCritic", "ObstaclesCritic", "GoalCritic", "GoalAngleCritic", "PathAlignCritic", "PathFollowCritic", "PathAngleCritic", "PreferForwardCritic"]
+      critics: ["ConstraintCritic", "CostCritic", "GoalCritic", "GoalAngleCritic", "PathAlignCritic", "PathFollowCritic", "PathAngleCritic", "PreferForwardCritic"]
       ConstraintCritic:
         enabled: true
         cost_power: 1
@@ -221,24 +221,24 @@ controller_server:
         cost_power: 1
         cost_weight: 5.0
         threshold_to_consider: 0.5
-      ObstaclesCritic:
-        enabled: true
-        cost_power: 1
-        repulsion_weight: 1.5
-        critical_weight: 20.0
-        consider_footprint: false
-        collision_cost: 10000.0
-        collision_margin_distance: 0.1
-        near_goal_distance: 0.5
-      # Option to replace Obstacles and use Cost instead
-      # CostCritic:
+      # ObstaclesCritic:
       #   enabled: true
       #   cost_power: 1
-      #   cost_weight: 3.81
-      #   critical_cost: 300.0
-      #   consider_footprint: true
-      #   collision_cost: 1000000.0
-      #   near_goal_distance: 1.0
+      #   repulsion_weight: 1.5
+      #   critical_weight: 20.0
+      #   consider_footprint: false
+      #   collision_cost: 10000.0
+      #   collision_margin_distance: 0.1
+      #   near_goal_distance: 0.5
+      CostCritic:
+        enabled: true
+        cost_power: 1
+        cost_weight: 3.81
+        critical_cost: 300.0
+        consider_footprint: true
+        collision_cost: 1000000.0
+        near_goal_distance: 1.0
+      PathAlignCritic:
       PathAlignCritic:
         enabled: true
         cost_power: 1