docs: added admin setting page documentation (#4641)

* docs: added admin setting page documentation

* add link from routes to settings page

www/docs/sidebars.js

@@ -107,6 +107,11 @@ module.exports = {
           label: "Admin UI Routes",
           id: "admin/routes",
         },
+        {
+          type: "doc",
+          label: "Admin Setting Pages",
+          id: "admin/setting-pages",
+        },
         {
           type: "doc",
           label: "Example: Create Onboarding",