rebase this chart on cnpg provided chart

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

@@ -0,0 +1,16 @@
+{{- $alert := "CNPGClusterPGDatabaseXidAgeWarning" -}}
+{{- if not (has $alert .excludeRules) -}}
+alert: {{ $alert }}
+annotations:
+  summary: CNPG Cluster has a number of transactions from the frozen XID to the current one.
+  description: |-
+    Over 300,000,000 transactions from frozen xid
+    on pod {{`{{`}} $labels.pod {{`}}`}}
+expr: |
+  cnpg_pg_database_xid_age > 300000000
+for: 1m
+labels:
+  severity: warning
+  namespace: {{ .namespace }}
+  cnpg_cluster: {{ .cluster }}
+{{- end -}}