Honor ks.spec.postBuild.substituteStrategy

Signed-off-by: Matheus Pimenta <matheuscscp@gmail.com>

internal/build/testdata/substitute-strategy/always.yaml

@@ -0,0 +1,9 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: test-ks
+  namespace: flux-system
+spec:
+  path: "./resources"
+  postBuild:
+    substituteStrategy: Always

internal/build/testdata/substitute-strategy/resources/configmap.yaml

@@ -0,0 +1,7 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-config
+data:
+  color: "${color:=blue}"
+  shape: "${shape:=square}"

internal/build/testdata/substitute-strategy/resources/kustomization.yaml

@@ -0,0 +1,4 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - configmap.yaml

internal/build/testdata/substitute-strategy/with-variables.yaml

@@ -0,0 +1,8 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: test-ks
+  namespace: flux-system
+spec:
+  path: "./resources"
+  postBuild: {}