Add italian 2-letter codes for provinces

[mircobabini]

In Italy there is an official 2-letter code standard to refer to states (which are provinces).

As shown here: https://github.com/woocommerce/woocommerce/blob/10f92ca09101cb119f1fe9ed37b4967b2940e17e/i18n/states.php#L703-L810