props to @escattone for the suggestion

- if a corresponding k8s namespace -> branch does not exist, offer to:
  - delete the namespace
  - add an annotation to keep the namespace. The next run of this script
    won't offer to delete the namespace, and a command will be displayed
    (but not run) to clear the annotation.
  - ignore the namespace
- if a corresponding k8s namespace -> branch DOES exist, don't do
  anything