Ability to restart a broken database upgrade

### 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?

Postgres

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

I recently encountered 90 minutes of downtime due to a pg:upgrade on my Postgres database that was stuck in "Provisioning". According to Heroku Support:

```After reviewing our internal logs, it appears that the process timed out during an attempt to prepare the database on a different cluster for an upgrade. Our automation detected the issue while upgrading and autocorrected itself.```

(Ticket 1627704)

Encountering 90 minutes of downtime with no recourse is rough, and the "automatic detection" doesn't seem to run often enough. It would be great to allow some insight into the status beyond just the one-word "Provisioning", and offer some way to cancel/revert/restart the upgrade process.