docs(planning-design): update reference implementation diagram

[TakaHoribe]

Description

• Update planning diagram for the reference implementation
  • Add elastic_band_smoother node

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[maxime-clem]

The out_of_lane module is missing from the behavior_velocity_planner but it was also missing in the previous picture.
If you prefer I can add it in a separate PR.

[TakaHoribe]

@maxime-clem Oops, sorry. It is merged by auto-merge. I hope you will add the out_of_lane in another PR!