fix(matrix): Add missing CLUSTER_NAME environment variable

apps/base/matrix/database.yaml

@@ -53,6 +53,11 @@ spec:
         value: "true"
       - name: PG_EXPORTER_CONSTANT_LABELS
         value: 'release=$(CLUSTER_NAME),namespace=$(POD_NAMESPACE)'
+      - name: CLUSTER_NAME
+        valueFrom:
+          fieldRef:
+            apiVersion: v1
+            fieldPath: metadata.labels['cluster-name']
 ---
 apiVersion: monitoring.coreos.com/v1
 kind: PodMonitor