Merge branch '442096-new-group-mardown-preview-route' into 'master'

Add new group level markdown_preview route

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145001



Merged-by: Heinrich Lee Yu <heinrich@gitlab.com>
Approved-by: Heinrich Lee Yu <heinrich@gitlab.com>
Co-authored-by: Mario Celi <mcelicalderon@gitlab.com>

config/routes.rb

@@ -259,6 +259,8 @@
     resources(:groups, only: [:index, :new, :create]) do
       # The constraints ensure that the `group_id` parameter in the URL allows for multiple levels
       # of subgroups, permitting both regular and encoded slashes (%2F).
+      # Deprecated in favor of /groups/*group_id/-/preview_markdown
+      # https://gitlab.com/gitlab-org/gitlab/-/issues/442218
       post :preview_markdown, constraints: { group_id: %r{#{Gitlab::PathRegex.full_namespace_route_regex.source}(%2F#{Gitlab::PathRegex.full_namespace_route_regex.source})*} }
     end
 

config/routes/group.rb

@@ -164,6 +164,8 @@
     resources :achievements, only: [:index, :new, :edit]
 
     resources :work_items, only: [:index, :show], param: :iid
+
+    post :preview_markdown
   end
 
   scope(