core: frontend: vehicle-setup: allow testing servo and relay outputs

[ES-Alexander]

Current behaviour

The PWM setup page has some parameters for configuring PWM and relay outputs, as well as motors, but only the motor outputs allow being tested. Testing servo and relay outputs currently requires a control station software or manual MAVLink messages, which is needlessly frustrating when you just want to check that an output is working as expected.

Expected or desired behaviour

Add a servo and relay testing section, similar to the existing motor test section, but without the requirement to arm the vehicle to use it. Could bring #1818 into it, with PWM limit params specified around the test bar, like

Prerequisites

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