Fix some N+1 queries in the GET /projects API

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2363

What does this MR do?

Before improvements:

• Unauthenticated user: N+1 problem on :route and :namespace

  • 5 requests for 1 project
  • 8 requests for 2 projects
  • => approximately 3 additional queries per project

• Authenticated user: N+1 problem on :route, :namespace, :project_members, and :group_member

  • No projects belongs to a group

    • 53 queries for 4 projects
    • 66 queries for 5 projects
    • => approximately 12 additional queries per project

  • Some projects belongs to a group

    • 67 queries for 5 projects
    • 81 queries for 6 projects
    • => approximately 12 additional queries per project

After improvements:

• Unauthenticated user: N+1 problem on :route and :namespace
  • always 5 requests
  • => no additional query per project
• Authenticated user: N+1 problem on :route, :namespace, :taggings, :project_members, and :group_member
  • No projects belongs to a group
    • 46 queries for 4 projects
    • 55 queries for 5 projects
    • => 7 less "bootstrap" queries, 3 less additional queries per project (still 8 additional queries per project)
  • Some projects belongs to a group
    • 55 queries for 5 projects
    • 64 queries for 6 projects
    • => 12 less "bootstrap" queries, 3 less additional queries per project (still 8 additional queries per project)

Are there points in the code the reviewer needs to double check?

• There are still N+1 queries but I couldn't improve them in a reasonable time.
• I don't think we need a changelog entry for such backstage change?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #33748 (closed)