restructure existing secret configuration

fleet.yaml

@@ -4,9 +4,6 @@ helm:
   repo: https://charts.bitnami.com/bitnami
   chart: postgresql
   version: 12.12.4
-  values:
-    auth:
-      existingSecret: "postgresql-auth"
 targetCustomizations:
   - name: istio
     clusterSelector:
@@ -17,13 +14,13 @@ targetCustomizations:
         primary:
           podAnnotations:
             proxy.istio.io/config: '{ "holdApplicationUntilProxyStarts": true }'
-  - name: loki-1
+  - name: postgres-existing-secret
     clusterSelector:
       matchLabels:
-        name: loki-1
+        postgres-existing-secret: "true"
     helm:
       values:
         auth:
-          existingSecret: null
+          existingSecret: "postgresql-auth"
 dependsOn:
   - name: cinder-csi