better avoidance drivable areas extension in behavior path planning: Remaining TODO

[zulfaqar-azmi-t4]

Remaining TODO:

1. Code refactoring (removing unnecessary function and make code more concise)
   1. refactor(avoidance_module): change implementation to lambda #486 -- DONE
2. Create debug new drivable area debug visualization to show extendable areas (allows us to see which areas which has 2 lanelets but the linestring is not shared.
   1. feat(behavior_path_planner): add drivable area visualization to observe shared linestring #499
3. Visualization improvement.
4. documentation edit

Related

1. The implementation feat(route_handler): better avoidance drivable areas extension in behavior path planning #285
2. Bug fix fix(behavior_path_planner): crash when drivable area expanding #365

[zulfaqar-azmi-t4]

Adding debug message to show reason for failure.
This is to simplify debugging on field as the field integrator members can just echo the message directly using ros2 topic echo.

[zulfaqar-azmi-t4]

Since the debug messages is already included in the avoidance module, the TODO list is considered completed.