簡単に任意のコントーラアクションを追加できる

# 任意のアクションを追加できる
```rb
  resources :photos do
    member do
      get "preview"
    end
  end
```
```
Prefix Verb   URI Pattern                                                                                       Controller#Action
                           preview_photo GET    /photos/:id/preview(.:format)                                                                     photos#preview
                                  photos GET    /photos(.:format)                                                                                 photos#index
                                         POST   /photos(.:format)                                                                                 photos#create
                               new_photo GET    /photos/new(.:format)                                                                             photos#new
                              edit_photo GET    /photos/:id/edit(.:format)                                                                        photos#edit
                                   photo GET    /photos/:id(.:format)                                                                             photos#show
                                         PATCH  /photos/:id(.:format)                                                                             photos#update
                                         PUT    /photos/:id(.:format)                                                                             photos#update
                                         DELETE /photos/:id(.:format)                                                                             photos#destroy
```
```rb
  resources :photos do
    get "preview", on: :member
  end
```
```
  Prefix Verb   URI Pattern                                                                                       Controller#Action
                           preview_photo GET    /photos/:id/preview(.:format)                                                                     photos#preview
                                  photos GET    /photos(.:format)                                                                                 photos#index
                                         POST   /photos(.:format)                                                                                 photos#create
                               new_photo GET    /photos/new(.:format)                                                                             photos#new
                              edit_photo GET    /photos/:id/edit(.:format)                                                                        photos#edit
                                   photo GET    /photos/:id(.:format)                                                                             photos#show
                                         PATCH  /photos/:id(.:format)                                                                             photos#update
                                         PUT    /photos/:id(.:format)                                                                             photos#update
                                         DELETE /photos/:id(.:format)                                                                             photos#destroy
                                         GET    /photos/:id/preview(.:format)                                                                     photos#preview
                                         GET    /photos(.:format)                                                                                 photos#index
                                         POST   /photos(.:format)                                                                                 photos#create
                                         GET    /photos/new(.:format)                                                                             photos#new
                                         GET    /photos/:id/edit(.:format)                                                                        photos#edit
                                         GET    /photos/:id(.:format)                                                                             photos#show
                                         PATCH  /photos/:id(.:format)                                                                             photos#update
                                         PUT    /photos/:id(.:format)                                                                             photos#update
                                         DELETE /photos/:id(.:format)                                                                             photos#destroy
```
```rb
  resources :photos do
    get "preview"
  end
```
```
 Prefix Verb   URI Pattern                                                                                       Controller#Action
                           photo_preview GET    /photos/:photo_id/preview(.:format)                                                               photos#preview
                                  photos GET    /photos(.:format)                                                                                 photos#index
                                         POST   /photos(.:format)                                                                                 photos#create
                               new_photo GET    /photos/new(.:format)                                                                             photos#new
                              edit_photo GET    /photos/:id/edit(.:format)                                                                        photos#edit
                                   photo GET    /photos/:id(.:format)                                                                             photos#show
                                         PATCH  /photos/:id(.:format)                                                                             photos#update
                                         PUT    /photos/:id(.:format)                                                                             photos#update
                                         DELETE /photos/:id(.:format)                                                                             photos#destroy
```

https://railsguides.jp/routing.html#%E3%83%AB%E3%83%BC%E3%83%86%E3%82%A3%E3%83%B3%E3%82%B0%E3%81%AE%E3%80%8Cconcern%E3%80%8D%E6%A9%9F%E8%83%BD:~:text=2.10%20RESTful%E3%81%AA%E3%83%AB%E3%83%BC%E3%83%86%E3%82%A3%E3%83%B3%E3%82%B0%E3%82%92%E3%81%95%E3%82%89%E3%81%AB%E8%BF%BD%E5%8A%A0%E3%81%99%E3%82%8B