New Flight Mode

Hello,
I'm trying to do a new flight mode, in order to facilitate passage of ambulances and other emergency vehicles. That's why I want to create a flight mode that do that my drone stays always a certain distance from me or a vehicle (for example 100 meters). I will use a telemetry module with my mobile, and a U-Blox 6M NEO GPS in my drone. The idea is to set some waypoints with the Tower App, and then through this "New Flight Mode", do that the drone stays always these 100 meters (radius) from me or vehicle. See please the image below to undestand the situation easier
Could someone help me to create this new mode?
Thank you so much,
David

The issue names no Mission Planner file, test, or entry point. Start by clarifying how Tower App waypoints, telemetry, and the U-Blox 6M NEO GPS would support the proposed mode. Done would need an agreed design and demonstrated behavior keeping the drone within the requested radius of a person or vehicle while following waypoints.

Written by the indexing model from the issue text.