DEV: Do not auto-generate plugin routes for admin experimental sidebar (#24211)

Followup to b53449eac9, we cannot
generate the links to plugin admin pages in this way because it
depends on which plugins are installed; we would need to somehow
do it at runtime. Leaving it out for now, for people who need to
find these admin routes the Ember Inspector extension for Chrome
can be used in the meantime.

app/assets/javascripts/admin/addon/components/admin-config-area-sidebar-experiment.hbs

@@ -13,7 +13,8 @@
     <code>icon</code>
     or a
     <code>href</code>, if you want to link to a specific page but don't know the
-    Ember route.</p>
+    Ember route. You can also use the Ember Inspector extension to find route
+    names, for example for plugin routes which are not auto-generated here.</p>
 
   <DButton
     @action={{this.resetToDefault}}