proposal: scheduled tasks (CronJob)

[atkrad]

#17 covers one-shot tasks (preDeploy, postDeploy, manual). Nightly cleanup and reports need a schedule.

Add "on": schedule (or a schedule: field) that renders a Kubernetes CronJob. Reuse task fields: from, image, command, resources, profiles, fanout.

tasks:
  cleanup:
    from: api
    "on": schedule
    schedule: "0 3 * * *"
    command: ["cleanup"]
    # concurrencyPolicy: Forbid

Validate the cron expression. No Service, Ingress, health, or HPA. The chart already has CronJob scaffolding; wire it to the task path.

Do not fold this into #17. A hook Job and a CronJob have different lifecycles. KEDA's cron scaler (#25) is replica schedules, not this.

Related: #17.