ClickHouse Managed Postgres backend guide

[sdairs]

Hi 👋 I work at ClickHouse. Would you be open to a backend guide for ClickHouse Managed Postgres?

I've prepared a short guide for Astro sites that need to query a managed PostgreSQL database. It uses the Node.js adapter and pg, covers the connection details and verified TLS, and finishes with a query from an Astro page.

I saw that new full guides need approval or a published stub first, so I'm checking the fit here before opening a PR. I'm happy to start with a stub if that's the better route.