Test Set schedules

Getting a test set to run on a recurring cadence used to mean wiring up your own CI job to trigger it on a cron. Now Thunders can do that natively.

• No CI required: schedule a test set to run on a recurring cadence directly from Thunders.
• Vary the run: schedule the same set across different environments, personas, or both.
• Managed right where you already work: schedules live on the test set itself, next to its regular run history.

A regression suite no longer needs a CI job of its own just to run on a schedule.

#Sprint31