Add support for HTU21d

[falcald]

Hardware details
Please add support to the HTU21D humidity and temperature sensor. It has a I2C communication and is very very similar to AHT20.
Datasheet: https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/171/1899_5F00_HTU21D_5F00_chip_5F00_datasheet.pdf

Benefits
It is a commonly used humidity sensor.

Python library
adafruit-circuitpython-htu21d

Context
The sensor module would be very similar to the AHT20 module.

Thanks!