First draft of API to add items to a collection (#37222)

config/routes/api.rb

@@ -12,7 +12,9 @@ namespace :api, format: false do
 
     resources :async_refreshes, only: :show
 
-    resources :collections, only: [:show, :create, :update, :destroy]
+    resources :collections, only: [:show, :create, :update, :destroy] do
+      resources :items, only: [:create], controller: 'collection_items'
+    end
   end
 
   # JSON / REST API