Restore sub-nav (Activity) for empty project

What does this MR do?

• Restore sub-nav which includes "Activity" tab for empty_repo view

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

• Unclear whether "Cycle Analytics" should be displayed with a empty project (seems to be fine to me)

I think this regressed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9272

Why was this MR needed?

All sub-nav items were missing, "Home", "Activity", "Cycle Analytics"

Screenshots (if relevant)

Before	After

Does this MR meet the acceptance criteria?

• 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 #29577 (closed)