DEV: Initial parts for a redesigned /about page (#27996)

This commit introduces the foundation for a new design for the /about page that we're currently working on.  The current version will remain available and still be the default until we finish the new version and are ready to roll out. To opt into the new version right now, add one or more group to the `experimental_redesigned_about_page_groups` site setting and members in those groups will get the new version.

Internal topic: t/128545.

app/serializers/current_user_serializer.rb

@@ -77,7 +77,8 @@ class CurrentUserSerializer < BasicUserSerializer
              :can_view_raw_email,
              :use_glimmer_topic_list?,
              :login_method,
-             :show_experimental_flags_admin_page
+             :show_experimental_flags_admin_page,
+             :render_experimental_about_page
 
   delegate :user_stat, to: :object, private: true
   delegate :any_posts, :draft_count, :pending_posts_count, :read_faq?, to: :user_stat
@@ -146,6 +147,10 @@ class CurrentUserSerializer < BasicUserSerializer
     object.in_any_groups?(SiteSetting.experimental_flags_admin_page_enabled_groups_map)
   end
 
+  def render_experimental_about_page
+    object.in_any_groups?(SiteSetting.experimental_redesigned_about_page_groups_map)
+  end
+
   def include_show_experimental_flags_admin_page?
     object.admin?
   end