Make Kustomize manifests more modular

kustomize/app/kustomization.yaml

@@ -0,0 +1,8 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+namespace: toy
+resources:
+  - deployment.yaml
+  - services.yaml
+  - ingress.yaml

kustomize/kustomization.yaml

@@ -3,6 +3,5 @@ apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 namespace: toy
 resources:
-  - deployment.yaml
+  - namespace.yaml
-  - services.yaml
+  - ./app
-  - ingress.yaml

kustomize/namespace.yaml

@@ -0,0 +1,6 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: toy
+