rebase this chart on cnpg provided chart

charts/postgres-cluster/prometheus_rules/cluster-high_replication_lag.yaml

@@ -0,0 +1,19 @@
+{{- $alert := "CNPGClusterHighReplicationLag" -}}
+{{- if not (has $alert .excludeRules) -}}
+alert: {{ $alert }}
+annotations:
+  summary: CNPG Cluster high replication lag
+  description: |-
+    CloudNativePG Cluster "{{ .namespace }}/{{ .cluster }}" is experiencing a high replication lag of
+    {{ .value }}ms.
+
+    High replication lag indicates network issues, busy instances, slow queries or suboptimal configuration.
+  runbook_url: https://github.com/cloudnative-pg/charts/blob/main/charts/cluster/docs/runbooks/CNPGClusterHighReplicationLag.md
+expr: |
+  max(cnpg_pg_replication_lag{namespace="{{ .namespace }}",pod=~"{{ .podSelector }}"}) * 1000 > 1000
+for: 5m
+labels:
+  severity: warning
+  namespace: {{ .namespace }}
+  cnpg_cluster: {{ .cluster }}
+{{- end -}}