feat(matrix): Add labels to postgresql exporter metrics

This patch adds some additional labels, that make it work better with
the dashboard provided by the postgres-system namespace.

apps/base/matrix/database.yaml

@@ -51,6 +51,8 @@ spec:
         value: "$(POSTGRES_PASSWORD)"
       - name: "PG_EXPORTER_AUTO_DISCOVER_DATABASES"
         value: "true"
+      - name: PG_EXPORTER_CONSTANT_LABELS
+        value: 'release=$(CLUSTER_NAME),namespace=$(POD_NAMESPACE)'
 ---
 apiVersion: monitoring.coreos.com/v1
 kind: PodMonitor