Add Wiki side bar to Overview page on wiki-only projects

Problem to solve

If you create a project that consists of Wiki only (via removing all other features in the project settings) we display the content of the initial "Home" Wiki page on the project Details page, which is great. However, we don't display the generated sidebar TOC, so if there are additional pages, you would need to manually add the TOC to the Home page content to achieve a useful default page.

Further details

https://gitlab.com/akaemmerle/example-project-wiki-only01

Proposal

Add the sidebar from /wiki to the project landing page as well.

What does success look like, and how can we measure that?

(If no way to measure success, link to an issue that will implement a way to measure this)

Links / references