To upload a document to a case:

• upload the document as a File using the endpoint POST api/files and keep the file's id returned by the response
• use the endpoint POST api/documents to attach the file to the intended entity in Ondorse
  • file_id is the file's id
  • attached to:
    • use application_id to attach it the case directly
    • use person_id to attach it to a related person of the case and business_id to a related business