Docs release 16.8

What does this MR do and why?

Because GitLab 16.8 has been released (https://about.gitlab.com/releases/2024/01/18/gitlab-16-8-released/), let's release the docs for it.

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.