Support Wiki with UTF-8 page name

What does this MR do?

Support Wiki with UTF-8 page name.

See https://github.com/gollum/gollum/pull/929

Why was this MR needed?

Relax constraints for wiki slug in aac65984.

It allows to create a wiki with UTF-8 name, but creating a wiki with UTF-8 name causes 500 error.

Creating a wiki with UTF-8 name once, then creating or updating wiki with ascii name also cause 500 error i.e. no one can create and update any wiki pages in the project.

Workaround

1. Go to https://DOMAIN/repo/wikis/git_access -> this page display the link to git clone
2. Clone the wiki repo
3. Find the page with UTF-8 name
4. Rename or Delete these files
5. Commit and push

What are the relevant issue numbers?

• #13979 (closed)
• #13891 (closed)
• #13698 (closed)
• #13603 (closed)
• #13317 (closed)
• #12906 (closed)
• #12825 (closed)
• #10945 (closed)

Todo

• Waiting for 'gollum-rugged_adapter' that support rugged v0.24.0 release

'gollum-rugged_adapter' gem doesn't allow to install rugged v0.24.0 (it's still beta version), but 'gitlab_git' gem depends on rugged v0.24.0b13.

So it can't install both 'gollum-rugged_adapter' and 'gitlab_git' now.