rebase this chart on cnpg provided chart

charts/postgres-cluster/prometheus_rules/cluster-low_disk_space-critical.yaml

@@ -0,0 +1,24 @@
+{{- $alert := "CNPGClusterLowDiskSpaceCritical" -}}
+{{- if not (has $alert .excludeRules) -}}
+alert: {{ $alert }}
+annotations:
+  summary: CNPG Instance is running out of disk space!
+  description: |-
+    CloudNativePG Cluster "{{ .namespace }}/{{ .cluster }}" is running extremely low on disk space. Check attached PVCs!
+  runbook_url: https://github.com/cloudnative-pg/charts/blob/main/charts/cluster/docs/runbooks/CNPGClusterLowDiskSpaceCritical.md
+expr: |
+  max(max by(persistentvolumeclaim) (1 - kubelet_volume_stats_available_bytes{namespace="{{ .namespace }}", persistentvolumeclaim=~"{{ .podSelector }}"} / kubelet_volume_stats_capacity_bytes{namespace="{{ .namespace }}", persistentvolumeclaim=~"{{ .podSelector }}"})) > 0.9 OR
+  max(max by(persistentvolumeclaim) (1 - kubelet_volume_stats_available_bytes{namespace="{{ .namespace }}", persistentvolumeclaim=~"{{ .podSelector }}-wal"} / kubelet_volume_stats_capacity_bytes{namespace="{{ .namespace }}", persistentvolumeclaim=~"{{ .podSelector }}-wal"})) > 0.9 OR
+  max(sum by (namespace,persistentvolumeclaim) (kubelet_volume_stats_used_bytes{namespace="{{ .namespace }}", persistentvolumeclaim=~"{{ .podSelector }}-tbs.*"})
+      /
+      sum by (namespace,persistentvolumeclaim) (kubelet_volume_stats_capacity_bytes{namespace="{{ .namespace }}", persistentvolumeclaim=~"{{ .podSelector }}-tbs.*"})
+      *
+      on(namespace, persistentvolumeclaim) group_left(volume)
+      kube_pod_spec_volumes_persistentvolumeclaims_info{pod=~"{{ .podSelector }}"}
+  ) > 0.9
+for: 5m
+labels:
+  severity: critical
+  namespace: {{ .namespace }}
+  cnpg_cluster: {{ .cluster }}
+{{- end -}}