alerts-fux: add alert for blackbox exporter probes

resources/chaosknoten/grafana/docker_compose/prometheus_alerts-fux.rules.yaml

@@ -10,6 +10,15 @@ groups:
         annotations:
           summary: Job {{ $labels.job }} flaky on (instance {{ $labels.instance }})
           description: "The job {{ $labels.job }} on target: {{ $labels.instance }} has been flaky over the last 24 hours."
+      - alert: ProbeFailed
+        expr: group by(instance, job, ip) (probe_success{org="fux"} == 0)
+        for: 1m
+        labels:
+          severity: critical
+          org: fux
+        annotations:
+          summary: "Probe failed for {{ $labels.instance }} (job: {{ $labels.job }})"
+          description: "The Probe: {{ $labels.job }} can not complete its job for {{ $labels.instance }}, this most likely means that the instance is unreachable."
   - name: Fux-SNMP
     rules:
       - alert: SnmpTargetMissing