fix(alerts): add minio disk alerts

k8s/manifests/system-monitoring/kube-prometheus-stack/prometheus-rules/services/minio.yaml

@@ -18,3 +18,19 @@ spec:
             description: "Minio is experiencing increased S3 errors.  Operations
               may not occur as expected, and service may be impacted"
             summary: "Minio is experiecing elevated S3 errors."
+        - alert: MinioDiskOffline
+          expr: minio_disks_offline > 0
+          for: 0m
+          labels:
+            severity: critical
+          annotations:
+            summary: Minio disk offline (instance {{ $labels.instance }})
+            description: "Minio disk is offline\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"
+        - alert: MinioDiskSpaceUsage
+          expr: disk_storage_available / disk_storage_total * 100 < 10
+          for: 0m
+          labels:
+            severity: warning
+          annotations:
+            summary: Minio disk space usage (instance {{ $labels.instance }})
+            description: "Minio available free space is low (< 10%)\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"