Include nested groups items into search results

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/services/search/global_service.rb

@@ -9,7 +9,11 @@ module Search
     def execute
       group = Group.find_by(id: params[:group_id]) if params[:group_id].present?
       projects = ProjectsFinder.new.execute(current_user)
-      projects = projects.in_namespace(group.id) if group
+
+      if group
+        ids = group.descendants.push(group.id)
+        projects = projects.in_namespace(ids)
+      end
 
       Gitlab::SearchResults.new(current_user, projects, params[:search])
     end