Update wiki sidebar

What does this MR do and why?

• Truncate page names
• Remove button hover style
• Remove double border on sidebar
• Add button to view all pages

Screenshots or screen recordings

Before	After

How to set up and validate locally

• http://127.0.0.1:3000/gitlab-org/gitlab-test/-/wikis/home
• Test out a wiki with existing pages
• Test out a wiki with no pages yet (go to create form)

Links

• ✂️ UX Paper Cuts 17.1 → Wiki (#452225)