Use leds to indicate state

[smaerup]

No description provided.

[larsgk]

Good idea to have LED indicators... however, maybe we can have 2 small adjustments:

1. we need guards around all GPIO/LED code so it compiles and runs on devices that don't have the config
2. maybe we can consider to have the RGB PWM code from https://github.com/larsgk/simple-web-zephyr/blob/main/app/src/rgb_led.c (if we want some more color/effect options... I was actually considering to introduce that)

[larsgk]

We should guard the code on devices that don't have the GPIO/LED config