vehicle-setup: pwm-outputs: allow testing all configured motors

[ES-Alexander]

Current behaviour

ArduSub support is hardcoded to motors 1-8, which prevents testing additional motors.

Desired by at least this forum user, and presumably any others who are using BlueOS with a custom Sub vehicle that has more than 8 motors.

Expected or desired behaviour

Allow testing all connected motors that are supported by ArduSub's parameters.

For now that's 1-12, though in future (with scripting-based motor support) we may want a more generic approach than hardcoded parameter values...

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.