boards: shields: Add MikroElektronika Weather Click shield

Add a shield definition for the MikroElektronika Weather Click board.

The Weather Click board features the BME280 sensor, a combined humidity,
pressure, and temperature sensor from Bosch Sensortec.

This shield can be used with any board equipped with a mikroBUS socket
that provides a `mikrobus_i2c` devicetree node label.

Signed-off-by: Chris Wilson <chris@cgnd.dev>