[devkit] RGB LED support

[lure23]

Ideally, would like to:

• have async function for setting the LED by both its RGB or HSV values
• have easing functions that change the colors non-linearly; in the "background"

First step to this would be to have the current community sample compile (and run).

Then:

•  adopt the hello_rgb sample

[lure23]

Got the sample adopted.

Keeping the issue for the async color transitions.