Redirect project.wiki.git to project wiki home

What does this MR do?

This MR adds a redirect from namespace/project.wiki.git to namespace/project/wikis.

When a user has cloned the wiki repository, the remote URIs are visible as:

➜  wiki.wiki git:(master) git remote -v
origin	https://gitlab.com/namespace/project.wiki.git (fetch)
origin	https://gitlab.com/namespace/project.wiki.git (push)

This redirect brings expected behaviour when visiting the .git path, similar to how visiting the main repository displays the project page.

https://gitlab.com/gitlab-org/gitlab-ce/issues/19186

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers