rebase this chart on cnpg provided chart

charts/postgres-cluster/prometheus_rules/cluster-replica_failing_replication-warning.yaml

@@ -0,0 +1,16 @@
+{{- $alert := "CNPGClusterReplicaFailingReplicationWarning" -}}
+{{- if not (has $alert .excludeRules) -}}
+alert: {{ $alert }}
+annotations:
+  summary: CNPG Cluster has a replica is failing to replicate.
+  description: |-
+    Replica {{`{{`}} $labels.pod {{`}}`}}
+    is failing to replicate
+expr: |
+  cnpg_pg_replication_in_recovery > cnpg_pg_replication_is_wal_receiver_up
+for: 1m
+labels:
+  severity: warning
+  namespace: {{ .namespace }}
+  cnpg_cluster: {{ .cluster }}
+{{- end -}}