Add scheduled/cron service mode for periodic tasks

[jongio]

Feature Request

Problem

There's currently no way to define a service that runs on a schedule (e.g., every N minutes/hours). The existing service modes cover continuous processes (daemon), one-time tasks (task), file watchers (watch), and builds (build), but periodic/scheduled execution requires workarounds like writing a daemon with an internal sleep loop.

Proposal

Add a scheduled service mode (or a schedule field) that accepts a cron expression or interval, allowing services to run periodically as part of azd app run.

Example:

services:
  cleanup:
    type: process
    mode: scheduled
    schedule: "0 */6 * * *"  # Every 6 hours
    command: python scripts/cleanup.py
    healthcheck: false

Or with interval shorthand:

services:
  sync:
    type: process
    mode: scheduled
    schedule: "every 30m"
    command: ./scripts/sync.sh

Use Cases

• Periodic data exports or imports
• Cache warming / invalidation
• Log rotation or cleanup scripts
• Health report generation
• Database maintenance tasks (vacuum, reindex)
• Scheduled backups

Behavior

• Service shows in dashboard with next-run countdown
• Logs from each execution are captured like any other service
• Exit code tracked per execution (success/failure history)
• mode: scheduled implies type: process (no port needed)
• Missed schedules during downtime: configurable (skip or run-on-start)

Alternatives Considered

• Daemon with internal loop: Works but pushes scheduling logic into every script
• OS-level cron/Task Scheduler: Outside azd-app's visibility, no dashboard integration, no log aggregation
• Container with cron: Heavy for simple scripts