samples/boards: Add ArgonKey test

Test ArgonKey board. It provides an example of how to test
all the sensors on-board. It currently enables by default
following sensors:

   LPS22HB pressure/temp
   HTS221 humidity
   LSM6DSL accel/gyro plus LIS2MDL magn connected to it.
   VL53L0x proximity

Signed-off-by: Armando Visconti <armando.visconti@st.com>