Multiregion support for Heroku Control Plane (API)

### 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?

Control Plane (API)

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

Heroku's Control Plane (API) currently only has public ingress through a single region: `virginia`. There is no redundancy or failover. If `virginia` is experiencing severe enough issues, the Heroku API is down worldwide.

This means that in a multi-region hot/warm system, each region must run a formation of dynos capable of supporting 100% of the system's traffic since it would not be possible to scale `oregon` up in response to a failover to that region. This is not feasible and in many cases extremely wasteful.

The Heroku API should support optional parameters (in both the CLI and API directly) to make requests to a particular region, allowing a bypass of `virginia` in the case of an outage.

For example:

`heroku ps:scale web=3 -a my-prd-service-rw-or --region=oregon`