Show directory hierarchy when listing wiki pages

What does this MR do?

This MR changes the visualization of the list of pages of a wiki. With this change, the directory structure also becomes visible.

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

No.

Why was this MR needed?

It makes finding files in complex wikis easier (because the user can now look for specific directories). It also helps to differentiate files that have the same name but belong to different directories (and potentially have very different contents).

Screenshots (if relevant)

When analyzing the changes bellow, please have in mind a Wiki with the following structure (designed to include a lot of relevant scenarios):

Wiki pages sidebar (before)

Wiki pages sidebar (after, including the new breadcrumb component)

Wiki pages listing (before)

Wiki pages listing (after)

Add new wiki page (before)

Add new wiki page (after)

Does this MR change any css classes?

Yes, it does. Bellow, the classes changed and the affected pages:

.wiki-last-edit-by

• ./app/views/projects/wikis/show.html.haml: %span.wiki-last-edit-by

.wiki-pages

• ./app/views/projects/wikis/_sidebar.html.haml: %ul.wiki-pages

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• 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 #23535 (closed)

Next steps

Please see my newest comment on this MR. Thank you.

I am looking forward for your feedback (@smcgivern / @DouweM). Thanks!