bluetooth: gatt: Add GAP Central Address Resolution characteristic

This adds Central Address Resolution characteristic that is required
to check by peer if it's about to send directed advertisements where
initiator address is set to RPA.
Zephyr supports the Address Resolution, so the characteristic value
is hard-coded.
Please check Core 5.0 Vol 3 Part C 12.4 CENTRAL ADDRESS RESOLUTION
Related PTS test case: GAP/CONN/ACEP/BV-03-C

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>