external-secrets: upgrade to 0.15.1

One minor at a time from 0.10.7 to 2.13.0, see docs/upgrade-k8s-1.33.md.

apps/templates/external-secrets-helm.yaml

@@ -17,7 +17,7 @@ spec:
   sources:
     - chart: external-secrets
       repoURL: https://charts.external-secrets.io
-      targetRevision: 0.14.4
+      targetRevision: 0.15.1
   destination:
     server: https://kubernetes.default.svc
     namespace: external-secrets