SQL performance improvements for ProjectsController#show

What does this MR do?

This adds various improvements to reduce the time spent in SQL queries in the ProjectsController#show method (and the views it calls).

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Reviewd
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/36878