Allow to generate panID by setting "pan_id: GENERATE". https://github.com/Koenkk/zigbee2mqtt/issues/5745

lib/zigbee.js

@@ -53,6 +53,12 @@ class Zigbee extends events.EventEmitter {
             herdsmanSettings.network.networkKey = newKey;
         }
 
+        if (herdsmanSettings.network.panID === 'GENERATE') {
+            const newPanID = Math.floor(Math.random() * (0xFFFF - 2)) + 1;
+            settings.set(['advanced', 'pan_id'], newPanID);
+            herdsmanSettings.network.panID = newPanID;
+        }
+
         try {
             herdsmanSettings.acceptJoiningDeviceHandler = this.acceptJoiningDeviceHandler;
             this.herdsman = new ZigbeeHerdsman.Controller(herdsmanSettings);