feat: Add a documentation layout design for public help center portal (#14403)

https://github.com/user-attachments/assets/fc4d15f9-2b54-4627-940f-94772ec739b1

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

app/models/portal.rb

@@ -46,7 +46,7 @@ class Portal < ApplicationRecord
 
   scope :active, -> { where(archived: false) }
 
-  CONFIG_JSON_KEYS = %w[allowed_locales default_locale draft_locales website_token].freeze
+  CONFIG_JSON_KEYS = %w[allowed_locales default_locale draft_locales website_token social_profiles layout].freeze
 
   def file_base_data
     {
@@ -94,6 +94,10 @@ class Portal < ApplicationRecord
     page_title.presence || name
   end
 
+  def layout
+    config_value('layout').presence || 'classic'
+  end
+
   private
 
   def config_json_format