Upgrade note - Adding GitLab 16.7 Geo secondary site

What does this MR do?

Postgres version 14 is the default Postgres verions for GitLab 16.7.0 onwards. Due to issue omnibus-gitlab#7768 (closed) Geo secondary sites cannot be upgraded to Postgres 14.

This MR highlights the options for customers wanting to deploy a Geo secondary site based on GitLab 16.7.

Based their configuration they will need to take the following actions:

• Adding your first Geo secondary site - Upgrade the Primary site to Postgres 14 before setting up the new Geo secondary site.
• Adding a new Geo secondary site to a deployment that already has one or more Geo secondaries: Install the new Geo secondary site with pinned postgres version 13. See Pin the packaged PostgreSQL version for more details.

Related issues

• omnibus-gitlab#7768 (closed)
• omnibus-gitlab#8288 (closed)

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
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• ~"frontend"
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These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

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