Add pg_uuidv7 to list of available Postgres extensions

### 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?

There are performance benefits to using UUID v7 verses UUID v4 for identity columns in Postgres ([see article](https://www.cybertec-postgresql.com/en/unexpected-downsides-of-uuid-keys-in-postgresql/)). The Postgres team also plans to add a function to create UUID v7 values in the upcoming version 17 ([link](https://commitfest.postgresql.org/46/4388/)). However, that won't be available for a while.

The [pg_uuidv7](https://pgxn.org/dist/pg_uuidv7/) Postgres extension adds a function to generate UUID v7 values. I would like to request that this extension be added to the list of available Postgres extensions so we can benefit from the performance gains of UUID v7 as we wait for Postgres version 17 to be available on Heroku Postgres.