Resolve "Add "Add Wiki" shortcut to the repository home page"

What does this MR do and why?

As proposed on the issue #366575 (closed), this MR adds a "Add Wiki" button on the repository home page in order to reduce the number of clicks required by a user to create a repository-level wiki page.

Screenshots and screen recordings

New flow with "Add Wiki" button

"Add Wiki" button on empty repository

How to set up and validate locally

1. Start GDK:

   gdk start

2. Sign in as root user.
3. Visit any project page.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #366575 (closed)