feat(strat_planner): add a prepare time for blinker before taking action for approval

Signed-off-by: Mamoru Sobue <mamoru.sobue@tier4.jp>

Author: soblin

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

@@ -38,6 +38,7 @@
       backward_path_update_duration: 3.0
       ignore_distance_from_lane_end: 15.0
       # turns signal
+      prepare_time_before_start: 3.0
       th_turn_signal_on_lateral_offset: 1.0
       intersection_search_length: 30.0
       length_ratio_for_turn_signal_deactivation_near_intersection: 0.5