Refactor: use K8sDeploymentConfig inside Deployment to generate kubernetes yamls

[alaeddine-13]

After Deployment is exposed to serve Executors, we want to use it in order to generate kubernetes yaml as well.
This means, the Deployment should use K8sDeploymentConfig to implement to_kubernetes_yaml.

Potentially, we also want to refactor Flow.to_kubernetes_yaml to use the new method and maybe the same for Executor (or deprecate Executor.to_kubernetes_yaml)