feat(promotion code): Promotion code system done

I added the features for users to use promotion code
and for promoters to create on their events.
May be rewrite to discount code?

config/routes.rb

@@ -91,6 +91,16 @@ Rails.application.routes.draw do
           post :duplicate
         end
       end
+
+      # Nested promotion codes routes
+      resources :promotion_codes, except: [ :show ]
+    end
+  end
+
+  # === Promotion Codes Routes ===
+  resources :promotion_codes, only: [ :index ] do
+    member do
+      post :apply
     end
   end