GHSA-RXRQ-FV76-26PR free5GC's NEF crashes via logger.Fatal on PFD notification delivery failure (attacker-controlled notifyUri)

Summary free5GC's NEF terminates the entire process when a stored PFD-subscription notifyUri cannot be reached. In PfdChangeNotifier.FlushNotifications, the notifier calls NnefPFDmanagementNotify... and on any delivery error invokes logger.PFDManageLog.Fatalerr, which is os.Exit1-equivalent in Go...