Turn off default timeout for PostgreSQL

Overview

In 12.9, we added support for using a default client timeout for PostgreSQL statements for external PostgreSQL databases. Prior to 12.9, a default timeout could only be set when using the PostgreSQL bundled with Omnibus.

Problem

gitlab.com uses an external database. The new default timeout is causing issues on .com due to the way it interacts with PgBouncer's transaction pool mode.

Proposal

To resolve concerns for .com, we should not set a timeout default on the client side for now. In a future release we can reimplement the timeout taking into consideration the suggestions in #5255 (closed).

We will need to update the docs and make a note of this in the release post.