Allow pins to be changed for pio usb

[andrewfstratton]

The Waveshare RP2040 Zero and One boards both have Pin 16 allocated to a NeoPixel, so being able to reconfigure the pin/s used for PIO USB would be useful.

It could also be useful to reconfigure the web enable pin - but that wouldn't be possible through the web interface :|

[Loc15]

It's easy to change pin configuration on code to do the build, just it's necessary to change header file with name config.h.
I could to do builds for other boards too if someone needs it. It's a good idea but there is another priorities.

[andrewfstratton]

Adafruit feather also uses pin 16 for an LED