overrides: enable variable substitution

basic/clusters/production/overrides-kustomization.yaml

@@ -11,3 +11,7 @@ spec:
   path: ./basic/overrides
   prune: true
   validation: client
+  postBuild:
+    substituteFrom:
+      - kind: Secret
+        name: stackspin-cluster-variables

basic/overrides/stackspin-nextcloud-override.yaml

@@ -21,7 +21,7 @@ data:
               'allow_user_to_change_display_name' => false,
               'default_phone_region' => 'DE',
               'default_locale' => 'en-gb',
-              'lost_password_link' => 'https://sso.ftt.gmbh/login/recovery',
+              'lost_password_link' => 'https://sso.${domain}/login/recovery',
             );
     apps:
       # Basics