[EE] Add users search results to global search

What does this MR do?

EE version of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21197

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer

app/services/search/global_service.rb

@@ -13,8 +13,13 @@ def initialize(user, params)
     end
 
     def execute
-      Gitlab::SearchResults.new(current_user, projects, params[:search],
-                                default_project_filter: default_project_filter)
+      if Gitlab::CurrentSettings.elasticsearch_search?
+        Gitlab::Elastic::SearchResults.new(current_user, params[:search],
+                                           elastic_projects, projects, elastic_global)
+      else
+        Gitlab::SearchResults.new(current_user, projects, params[:search],
+                                  default_project_filter: default_project_filter)
+      end
     end
 
     def projects