Fix autocomplete in wikis

What does this MR do and why?

Currently, autocomplete is completely broken in wikis. Wikis traditionally do not support quick actions, but rest of autocomplete items should work correctly. (Including members, issues, MRs, epics, etc.)

Screenshots or screen recordings

How to set up and validate locally

1. Open any wiki page
2. Type in @, ~, !, #, % etc to bring up respective autocomplete items (members, labels, MRs, issues, milestones etc)

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.

app/views/shared/wikis/edit.html.haml

 - wiki_page_title @page, @page.persisted? ? _('Edit') : _('New')
 - add_page_specific_style 'page_bundles/wiki'
+- @gfm_form = true
+- @noteable_type = 'Wiki'
 
 - if @error
   #js-wiki-error{ data: { error: @error, wiki_page_path: wiki_page_path(@wiki, @page) } }