function to add notification listeners to the Optimizely client

AppDelegate.swift

func addListeners() {
        let notificationCenter = optimizely.notificationCenter
            
            //notification fired when a value is returned by isFeatureEnabled function call
        _ = notificationCenter?.addDecisionNotificationListener(decisionListener: { (type, userId, attributes, decisionInfo) in
            print("Received decision notification: \(type) \(userId) \(String(describing: attributes)) \(decisionInfo)")
        })

            //notification fired when SDK polls for a new datafile and the datafile has changed
        _ = notificationCenter?.addDatafileChangeNotificationListener(datafileListener: { (_) in
            print("data file did change!")
        })
    }