Add a shared PostgreSQL database

[john-gom]

Problem

A number of project use PostgreSQL as their relational database. For production deployment we want to manage a single instance to simplify day to day management, backups, etc. Having a shared service for development and staging would more closely match this model.

Proposed solution

Add a PostgreSQL instance to the shared services

Design

We can use a bootstrap user, which just has permission to create databases and with less secure credentials, to create the database and read/write user for each project. This is already modelled in openfoodfacts-auth