We replace the usage of WikiPage::CreateService with the wiki_page factory in the specs.

Replaces all the explicit include metadata syntax in the specs (tag:
true) into the implicit one (:tag).
Added a cop to prevent future errors and handle autocorrection.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

1. So we can build the markdown preview URL for it.

2. We can't skip the slug in this case, because the slug is used to
construct relative markdown URLs.

3. Add rspec feature tests to cover creating wiki pages with
   spaces/hyphens in the name.

4. Add rspec feature tests for markdown preview URL rewriting, which was
   only covered by unit tests up to this point.