Simulation: use sim_vehicle's --list-models to populate the Model drop-down

This AP flight code SITL change moves some of the model setup to the C++ https://github.com/ArduPilot/ardupilot/pull/32918

It would be nice if we replaced MP's Model drop-down to take advantage of this

Start by reviewing the referenced ArduPilot pull request and the Mission Planner Model drop-down implementation. Investigate how sim_vehicle exposes --list-models and how Mission Planner currently obtains model choices. Done means the Model drop-down uses that model list reliably in SITL.

Written by the indexing model from the issue text.