Bluetooth: tester: Support pincode request for BR

Set the pin code request callback `auth_pincode_entry`.

If `highsec` is false, call `bt_conn_auth_pincode_entry` with pin code
"0000".
If `highsec` is true, call `bt_conn_auth_pincode_entry` with pin code
"0000000000000000".

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>