Usage Alerts

### 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?

Billing

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

Currently it can be hard for Heroku customers to be alerted of usage spikes or usage that's going to exceed subscriptions or licenses. We want to introduce the notion of automated and user-configurable alerts to help customers stay on top of usage.