Support all schedule types on PrefectDeployment

[chrisguidry]

Summary

Adds support for cron and rrule schedules to PrefectDeployment, completing support for all Prefect schedule types. The implementation uses Prefect's exact prefect.yaml syntax for seamless migration.

• ✅ Interval schedules: interval: 60, anchor_date: "2024-01-01T00:00:00Z"
• ✅ Cron schedules: cron: "* * * * *", day_or: true
• ✅ RRule schedules: rrule: "RRULE:FREQ=MINUTELY;INTERVAL=1"

Key Changes

• Flattened schedule structure to match Prefect's API format exactly
• Comprehensive validation ensuring exactly one schedule type per schedule
• HTTP status code fix accepting all 2xx responses (fixes 201 Created bug)
• Enhanced test coverage with 75+ test cases for all schedule types
• Perfect API compatibility with detailed field mapping comments
• Updated documentation with local testing procedures

Usage Example

apiVersion: prefect.io/v1
kind: PrefectDeployment
spec:
  deployment:
    schedules:
    # Cron schedule - exactly like prefect.yaml
    - slug: "daily-9am"
      cron: "0 9 * * *"
      timezone: "America/New_York"
      active: true
      
    # RRule schedule - RFC 5545 compliant
    - slug: "weekly-monday"
      rrule: "RRULE:FREQ=WEEKLY;BYDAY=MO"
      timezone: "UTC"
      active: true
      
    # Interval schedule - existing format
    - slug: "hourly"
      interval: 3600
      anchor_date: "2024-01-01T00:00:00Z"
      timezone: "UTC"
      active: true

Testing

• All 193 unit tests pass
• End-to-end validation with live Prefect API confirmed
• HTTP status code handling tested for 200, 201, 202, 204, 4xx, 5xx
• Example deployment in deploy/samples/deployment_end-to-end.yaml demonstrates all three schedule types

Closes #175

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[mitchnielsen]

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