Expose WiFi.setLEDs(r, g, b) through AdafruitIO_AIRLIFT class.

[ptbw]

The purpose of this change to to allow access to the setLEDs method in the WiFi class used by the Adafruit AirLift module. Making it very simple to add a status light to the class, and allow the visual inspection of the connection.

The change adds a single public method to the AdafruitIO_AIRLIFT class which is only available if included using #define USE_AIRLIFT or similar, so will only be available to specifically including ..IO_AIRLIFT.h

I made a small modification to the AdafruitIO_LEDTest example (supplying a colour from Adafruit.IO):

void handleMessage(AdafruitIO_Data *data) {
  // print RGB values and hex value
  Serial.println("Received HEX: ");
  Serial.println(data->value());

  int red = data->toRed();
  int grn = data->toGreen();
  int blu = data->toBlue();
  Serial.println(red);
  Serial.println(grn);
  Serial.println(blu);
  io.setLEDs( red, grn, blu);
}

The example builds when using #define USE_AIRLIFT in the supplied config.h.

[brentru]

@ptbw Thanks for making comments more explicit, I'll test on hardware and merge once it's passing the CI.

This PR is failing our CI build at the Clang step (https://github.com/adafruit/Adafruit_IO_Arduino/pull/133/checks?check_run_id=981225404#step:8:1).

[brentru]

I made a small modification to the AdafruitIO_LEDTest example (supplying a colour from Adafruit.IO):

@ptbw Do you want to add an example for this into examples? If not everything looks good and I can merge/release

[ptbw]

Go a head and merge, I can't really test any example on anything other than the Airlift feather wing. But I have learnt a lot from this so thank you for your patience.