Use envsubst in CI

.gitlab-ci.yml

@@ -44,5 +44,5 @@ deploy docker image:
     - echo $KUBECONFIG | base64 -d > /tmp/kubeconfig
     - cd deploy/overlays/production
     - kustomize edit set image registry.edugit.org/teckids/team-pr/teckids.org:$(cat ../../../DIGESTFILE)
-    - kustomize build -o output.yaml
+    - kustomize build | envsubst >output.yaml
     - kubectl --kubeconfig=/tmp/kubeconfig apply -f output.yaml