Output distance_to_destination metric from the planner and visualize it on RViz

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Feature Request: Distance to Destination Metric in Planner with RViz Visualization

Description

I propose the addition of a "distance_to_destination" metric output from the planner component in Autoware. This metric should represent the remaining distance to the destination for a vehicle at any given moment during its mission.

Furthermore, it would be incredibly useful to visualize this metric in RViz, offering real-time feedback on the distance left to travel.

Why This Would Be Useful

1. Enhanced Situational Awareness: Operators monitoring the vehicle's progress would benefit from a clear, quantifiable measure of how far the vehicle is from its destination, enhancing situational awareness.

2. Increased Safety: By continuously monitoring the distance to the destination, it's easier to identify discrepancies or deviations from the planned route early, potentially increasing safety through timely interventions.

3. User Experience: For end-users or passengers within autonomous vehicles, having access to this information can improve the user experience by setting clear expectations about the journey's duration.

Overall, the integration of a "distance_to_destination" metric and its visualization in RViz would bring substantial benefits in terms of operational efficiency, safety, and user satisfaction in Autoware's ecosystem.

(totally not written by chatgpt)

cc. @TakaHoribe @takayuki5168 @yukkysaito @mitsudome-r @mehmetdogru