sequenceDiagram
  participant Client
  participant Backend
  participant Storage
  Client->>Backend: POST rails/active_storage/direct_uploads
  Backend->>Backend: create ActiveStorage::Blob
  Backend->>Storage: url_for_direct_upload
  Storage-->>Backend: signed url
  Backend-->>Client: json with signed url
  Client->>Storage: PUT upload to signed url
  Client->>Backend: POST entity["image"]=key