Add Gitaly to the list of projects using docs Docker images

What does this MR do and why?

While working on: gitaly!5908 (merged), I realized we didn't have the gitaly project as a project to update when we update our Docker images.

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.