Add config files for running Postgres inside Docker Compose (#3637)

This PR adds config files for running the Postgres instance for local
Zed development in a Docker Compose instance.

For those of us who don't like to have a Postgres install always present
on the host system 😄

Usage:

```
docker compose up -d
```

Release Notes:

- N/A

docker-compose.sql

@@ -0,0 +1 @@
+create database zed;