Change local media attachments to perform heavy processing asynchronously (#13210)

Fix #9106

config/routes.rb

@@ -343,7 +343,7 @@ Rails.application.routes.draw do
         end
       end
 
-      resources :media,        only: [:create, :update]
+      resources :media,        only: [:create, :update, :show]
       resources :blocks,       only: [:index]
       resources :mutes,        only: [:index]
       resources :favourites,   only: [:index]
@@ -455,6 +455,7 @@ Rails.application.routes.draw do
     end
 
     namespace :v2 do
+      resources :media, only: [:create]
       get '/search', to: 'search#index', as: :search
     end