Fix a `wiki_page` factory instantiation for the case when project's namespace is a group

What does this MR do?

This revert a use of the wiki_page factory to use WikiPages::CreateService instead since WikiPages::CreateService passes the current_user when instantiating a ProjectWiki (i.e. project_wiki = ProjectWiki.new(@project, current_user)) while the wiki_page factory default to project.owner (i.e. @wiki ||= ProjectWiki.new(self, self.owner)).

Why was this MR needed?

Because master is broken.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #37729 (closed)