fix: support new schedule creation if not exist

[Hardikl]

This works. tried on vs_test svm as gold svm not exist.

On the u2 cluster, create a snapshot policy named every5hours on the vs_test SVM. The schedule is 5 hours and keeps the last 5 snapshots.

On the u2 cluster, create a snapshot policy named 10miuntes on the vs_test SVM. The schedule is PT10M and keeps the last 5 snapshots.

[Copilot]

Pull request overview

This PR adds support for automatically creating schedules when they don't exist during snapshot policy creation. Previously, if a referenced schedule didn't exist, the operation would fail with an error. Now, the code attempts to create the schedule by parsing its name to determine whether it follows an ISO 8601 interval format or a cron-style format.

Changes:

• Added automatic schedule creation fallback when a schedule doesn't exist in CreateSnapshotPolicy
• Implemented new CreateSchedule function that parses schedule names to determine format (ISO 8601 or cron-style)
• Extended Schedule and added Cron structs to support interval and cron-based schedule specifications

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 10 comments.

File	Description
rest/snapshotpolicy.go	Added CreateSchedule function with regex-based schedule name parsing, modified CreateSnapshotPolicy to call it when schedule is missing
ontap/ontap.go	Extended Schedule struct with Interval and Cron fields, added new Cron struct with time component fields

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[Hardikl]