v-m/alerts: Add alert for Internet down

victoria-metrics/alerts.yml

@@ -42,6 +42,16 @@ groups:
     expr: >-
       absent(collectd_nut_percent)
     for: 10m
+  - alert: Internet is down
+    expr: >-
+      probe_success{job="blackbox"} == 0
+    for: 5m
+    annotations:
+      severity: critical
+      summary: The connection to the Internet is down.
+      description: >-
+        The Internet connection is down.  Try rebooting the ONT, or call
+        Everfast Fiber.
 
 - name: Bitwarden
   rules: