Draft: Add pipeline execution policy schedule run

What does this MR do and why?

This makes it possible to run pipeline execution policies on a schedule.

There are multiple ways to implement this feature. In this MR I tried to re-use as much of the existing codebase as possible. It uses the Security::OrchestrationPolicyRuleSchedule model to store schedules.

Alternatives to this approach are:

• Use ci_pipeline_schedules
• Add a new table for pipeline execution schedules

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Related to #472671