Configure a Helm post-renderer using kustomize to inject sidecar containers and custom annotations into a third-party chart's output without forking the chart

Steps

1. Create a shell script named kustomize-post-renderer.sh that reads rendered Helm YAML from stdin, writes it to a temporary file, runs kustomize build pointing to a kustomization.yaml that patches the temporary file, and writes the result to stdout
2. Make the script executable and reference it in helm install or helm upgrade using the --post-renderer flag; Helm pipes its rendered manifests through the script before applying to the cluster
3. Write a kustomization.yaml that uses strategicMergePatch or JSON 6902 patch files to add a sidecar container to every Deployment in the rendered output, using a wildcard target selector
4. Add a commonAnnotations block in the kustomization.yaml to inject cost-center and team labels onto every resource regardless of type, avoiding the need to patch each resource individually
5. Combine the post-renderer with helm --post-renderer-args to pass environment-specific kustomization overlay directories, allowing the same base post-renderer script to apply different patches per environment
6. Validate the post-renderer output in CI by running helm template with the post-renderer and piping the result to kubeval or kubectl --dry-run=client to catch schema violations before deployment