Add support for INA219

[amotl]

In the spirit of #31, @rohlan signaled interest for supporting the INA219. For doing so, he already added the lowlevel driver the other day, see 71a5a1c.

The canonical URL to the MicroPython driver for INA219 by @chrisb2 is https://github.com/chrisb2/pyb_ina219.

See also https://community.hiveeyes.org/t/strom-und-spannung-mit-ina219-messen-und-messwerte-in-grafana-darstellen/2381.

[amotl]

Basic support for the INA219 has been added, see ina219_sensor.py and settings.example.py#L468-L475. While the code base supports it on MicroPython and CPython, it has only been tested on CPython so far. We will be happy to see others using and improving the implementation.

Thanks again @chrisb2 for conceiving and maintaining the lowlevel MicroPython driver and @deanm1278, @barbudor and @wallarug for conceiving and maintaining the @adafruit CircuitPython implementation.

cc @ClemensGruber, @MKO1640, @poesel, @thiasB, @rohlan, @wetterfrosch