FEATURE: the ability to expand/collapse all admin sections (#26358)

By default, admin sections should be collapsed.
In addition, a button to expand/collapse all sections has been added.

spec/system/page_objects/components/navigation_menu/sidebar.rb

@@ -40,6 +40,10 @@ module PageObjects
         def custom_section_modal_title
           find("#discourse-modal-title")
         end
+
+        def toggle_all_sections
+          find(".sidebar-toggle-all-sections").click
+        end
       end
     end
   end