Upgrade redis (persistent) gstg to Redis 6

Before we can get started with testing redis 6 on gstg, we need to ensure we have a published omnibus package containing the latest build (gitlab-org/omnibus-gitlab!4930 (merged)).

Nightly tags:

In the past we've written production change issues for this, as the failover procedure has quite a few manual steps.

We should go back and find one of those older change issues, to repurpose for this upgrade.

Edited by Igor