add missing postgresql variable to wire-server secrets templates

[Veki301]

Change type

• [x] Fix
• [ ] Feature
• [ ] Documentation
• [ ] Security / Upgrade

Basic information

• [x] THIS CHANGE REQUIRES A DEPLOYMENT PACKAGE RELEASE
• [ ] THIS CHANGE REQUIRES A WIRE-DOCS RELEASE

Testing

• [ ] I ran/applied the changes myself, in a test environment.
• [ ] The CI job attached to this repo will test it for me.

Tracking

• [ ] I mentioned this PR in Jira, OR I mentioned the Jira ticket in this PR.
• [ ] I mentioned this PR in one of the issues attached to one of our repositories.

Knowledge Transfer

• [ ] An Asciinema session is attached to the Jira ticket.

Motivation

Objective

Reason

Use case