template: add support for cleanup before deleting dag.

[kriyanshii]

introducing a new field in dag cleanup:. where you can mention any script(path to the script). So it will run that script while deleting the dag. It can be used to clean up intermediate files made while the dag ran.

steps:
  - name: "1"
    command: "true"
cleanup: "/path/to/script.sh"

[kriyanshii]

i would like to work on this.

[yohamta]

Thanks a lot! How would you like to implement it? I'd be grateful if you could share planning changes and design about this functionality. I'm still a bit unsure when the script should be called.