Support K8sApp by `pipectl init` in simplest

[t-kikuc]

What would you like to be added:

Support generating the simplest app.pipecd.yaml for KubernetesApp by pipectl init as a part of #4677

Details:

• QuickSync would be enough for the deployment strategy at first.
• To consider: Kustomize, Helm
• See the rfc https://github.com/pipe-cd/pipecd/discussions/4635

Why is this needed: Make it easier to begin using PipeCD for Kubernetes apps