Add a new callback structure for Bluetooth authentication
This struct is meant to replace the information-only
callbacks in bt_conn_auth_cb. The reason for this is that
due to the nature of bt_conn_auth_cb, it can only be registered
once. To allow mulitple users gain information about pairing
and bond deletions, this new struct is needed.
Samples, tests, etc. are updated to use the new struct.
Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>
