GPIO interface: sysfs deprecated, move to libgpiod

[daviderovell0]

At the moment we use the sysfs method to interact with GPIOs via the gpio-sysfs.h class. The interface is now old and deprecated, it should be replaced with something else. The best alternatives seems to be libgpiod, a C library coming with CLI utility tools that has been added to the Linux Kernel and therefore seems to be the safest in term of future support. Plus it doesn't add extra dependencies.

libgpiod in kernel.org: https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/about/

Useful info and discussions:

• https://lloydrochester.com/post/hardware/libgpiod-intro-rpi/
• https://forum.xojo.com/t/libgpiod-vs-pigpiod-vs-wiringpi/59853/10