feat(avoidance): use free steer policy for safety check

Signed-off-by: satoshi-ota <satoshi.ota928@gmail.com>

Author: satoshi-ota

autoware_launch/config/planning/scenario_planning/lane_driving/behavior_planning/behavior_path_planner/avoidance/avoidance.param.yaml

@@ -187,6 +187,7 @@
         time_horizon_for_rear_object: 10.0               # [s]
         delay_until_departure: 0.0                       # [s]
         # rss parameters
+        steering: "free"                                 # [-] select "fixed" or "free"
         expected_front_deceleration: -1.0                # [m/ss]
         expected_rear_deceleration: -1.0                 # [m/ss]
         rear_vehicle_reaction_time: 2.0                  # [s]