Ability to access Heroku Postgres over VPN (also applies to VPC Peering)

### 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 Postgres

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

Currently, we can create a VPN or Peering between a Heroku Private Space and AWS, or a VPN to a different network. These can only be used to access Dynos from the other network at the moment. It would be ideal if we could also use it to access Heroku Postgres. I believe the only blocker is resolving the Private IP address assigned to the Postgres instance. If this can be made available, we can add DNS records to point at it over the VPN/Peering.