Allow lane-level traffic sensor data without a defined road event

[j-d-b]

This PR resolves #225, specifically:

• Change the conformance of the road_event_id property on the TrafficSensorLaneData object from Required to Optional.

This change allows a producer to provide lane-level traffic data without needing the ID of a defined road event.

[j-d-b]

This PR is in draft state until #265 is merged.

[sknick-iastate]

A couple of comments:

Should the lane_data in the TrafficSensor Object also be updated. For the description you could possible use: A list of objects each describing traffic data for a specific lane whcih can be linked/associated with a road event lane and indicate the metrics of that lane. I think the notes can probably be removed entirely or softened significantly.

If someone doesn't know the road_event_id I'm not not sure how the lane_order can be used since it also refers to the road_event_id. My initial thought was just to soften the text to say that it corresponds to the road events Lane's if provided then copy the guidance from lane_order for those that do not know the road_event_id. But the issue with this is that it then limits the lane data to only a single direction since the count is from left to right. If both directions are provided the lane_order values will likely be repeated and make them indistinguishable by direction.

A few possible options I can think of to resolve this are:

• Provide guidance on a different methodology for the lane_order that counts the lanes from the sensor. I'm not a fan of this since I don't think we should modify the description of lane_order in different parts of the spec.
• Make the lane_order conditional and add a separate conditional lane numbering value if the road_event_id is not known. I don't know if this is a great option since it could be confusing and you still couldn't convey the different direction of travel. You would only be able to distinguish that different lanes are being collected
• Add a direction value that allows the two directions to be distinguished that is conditional (users should either provide a direction or road_event_id). This could be used with the original guidance of the lane_order and keep that required. This would be my preferred option as it is fairly simple and doesn't modify the original capability much.

[j-d-b]

Description changes to be made per co-chairs discussion 2022-08-04

TrafficSensorLaneData:

• Update lane_order description:
  • First sentence: change "road event" to "roadway";
  • Second sentence: change to "If the road_event_id is provided the value of this property corresponds to the associated road event's Lane's order property."

TrafficSensor:

• Remove "road event" language from description