None HA Private/Shield Postgres instances

### 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, all Private and Shield Postgres tiers are seemingly built on the Premium tier, offering features such as High Availability.

While this is ideal for production environments, it presents a challenge for private Development or Test environments, as these tiers also include High Availability, which likely contributes to higher costs.

It would be highly beneficial to have a Private/Shield tier of Postgres based on the Standard tier, providing a more cost-effective option for private Development and Test environments.