feat: Grouping the traffic lights

[plass-bertrandt]

Reference to a related issue in the repository

TrafficLight rework proposal. #754

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The individual bulbs of a traffic light rarely function as standalone signals. Rather, they form a unit consisting of two or three bulbs that convey a specific instruction to the driver.

The introduction of the group_id defines a unique assignment of the lights. It replaces heuristics—such as those based on position and orientation—that were previously necessary in the user software.

Some questions to ask:

• It's a new feature.
• Backward compatibility:

  IF group_id IS PRESENT:
      → Group bulbs by group_id
  ELSE:
      → Fall back to position-based / heuristic grouping (legacy)
  

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[tbleher]

Thank you @plass-bertrandt for posting this!

@pmai and @jdsika I would appreciate something like this in the next OSI standard (version 3.9). Grouping traffic lights has been a recurring problem whenever we have integrated traffic agents using OSI. Typically the grouping should be known by the simulation engine (at least lights are grouped in OpenDRIVE). It would be good if the simulation engine could forward this information e.g. to traffic agents.

I like the proposed solution since it is quite simple, but am open to other possibilities on how to represent this information.