Prepare for the disable `POSTGRES_ENABLED` change for 16.0

As part of 16.0 a new breaking change will set the Auto Deploy: disable POSTGRES_ENABLED by default. Related issue - gitlab-org/gitlab#343988 (closed)

From slack - @devin updated with

version.gitlab.com's production deployment already had this explicitly set to false, but the staging and review app deployments were relying on the default. I've manually set it to true there, so when the change lands it shouldn't break any pipelines. I'm not aware of any place else that this should bite us. The design app doesn't have a database, and most other things don't use auto devops.