Use patchesStrategicMerge for Kustomize patching

Drop for legacy patches was dropped [1] in `sigs.k8s.io/kustomize/api`
`v0.13.0`, causing Fleet acceptance tests for Kustomize examples to
fail.

[1]: https://github.com/kubernetes-sigs/kustomize/releases/tag/api%2Fv0.13.0

tests/expected/multi-cluster/kustomize/bundle.yaml

@@ -219,7 +219,7 @@ spec:
   - content: |
       resources:
       - ../../base
-      patches:
+      patchesStrategicMerge:
       - redis-slave-deployment.yaml
       - redis-slave-service.yaml
     name: overlays/dev/kustomization.yaml
@@ -259,7 +259,7 @@ spec:
   - content: |
       resources:
       - ../../base
-      patches:
+      patchesStrategicMerge:
       - frontend-deployment.yaml
       - frontend-service.yaml
     name: overlays/prod/kustomization.yaml
@@ -274,7 +274,7 @@ spec:
   - content: |
       resources:
       - ../../base
-      patches:
+      patchesStrategicMerge:
       - frontend-deployment.yaml
     name: overlays/test/kustomization.yaml
   targets: