CRON expressions in Procfile

### Required Terms

- [X] I agree to follow this project's [Code of Conduct](https://github.com/heroku/roadmap/blob/main/CODE_OF_CONDUCT.md)
- [X] I have read and accept the [Salesforce Program Agreement](https://www.salesforce.com/company/program-agreement/)

### What service(s) is this request for?

heroku dynos, scheduler

### Tell us about what you're trying to solve. What challenges are you facing?

We semi-frequently have issues with people forgetting to manually add/delete jobs in the heroku scheduler. On top of this, fiddling with these jobs manually though a webpage means we don't have any history of what things were scheduled nor when.

It would be way nicer if in the Procfile I could defined a schedule for jobs.
For example

```
refresh_purchase_suggestions: psql $DATABASE_URL -c "REFRESH MATERIALIZED VIEW product_purchase_data"
```
+ manually fiddling in the scheduler

would become

```
30 1 * * * psql $DATABASE_URL -c "REFRESH MATERIALIZED VIEW product_purchase_data"
```

That way, all the drawbacks mentioned in the top would be fixed, and schedule changes could be checked in pull requests, and viewed in the git log.