Schedule trigger in yaml spec

I want to spec a plan that just runs a simple script on a periodic/cron schedule. Ideally something this simple would be a yaml spec, but I can't specify a schedule trigger.

Something like this would work:

project:
  key: PIPE
  plan:
    key: MINISYNC
    :
    triggers:
    - schedule: every 30 minutes
    stage:
      job:
        scripts:
        - curl --silent ...etc.