bluetooth: smp: Add authentication callbacks per connection

Change introduces authentication callbacks used only for specified
BLE connection. The feature can be used by devices that require
reporting specific bonding capabilities only when pairing using
vendor-specific procedures.

If per-connection authentication callbacks are defined for given
connection, they are used instead of global authentication
callbacks. SMP latches authentication callbacks during the first
access to prevent updating the callbacks while pairing.

Fixes: #38336

Signed-off-by: Marek Pieta <Marek.Pieta@nordicsemi.no>