Allow staggering of cron workflows with identical schedules

# Summary

Allow cron workflow schedules to be set up in such a way that multiple workflows with identical schedules don't all start at the exact same time. This will prevent sudden surge in loads. Jenkins supports this feature, see [here](https://stackoverflow.com/questions/47302607/meaning-of-h-5-in-cron-jenkins) for a description.

# Use Cases

The controller could use this mechanism to stagger the launching of each workflow by a few seconds/minutes if there are cron workflows configured with identical schedules, for example, run once per day at 9 am.

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No files, tests, or entry points are identified in the issue. Start by tracing how the controller schedules cron workflows, then determine how identical schedules should be detected and staggered; done means configured workflows no longer launch simultaneously and existing scheduling behavior remains intact.

Written by the indexing model from the issue text.