add config for auto delete of offline nodes

scripts/netmaker.default.env

@@ -102,3 +102,7 @@ STUN=true
 METRICS_PORT=51821
 # Metrics Collection interval in minutes
 PUBLISH_METRIC_INTERVAL=15
+# auto delete offline nodes
+AUTO_DELETE_NODES=false
+# auto delete offline nodes interval in hours
+AUTO_DELETE_OFFLINE_NODES_INTERVAL=12