Create a file
Creates a file resource and returns the upload target for the bytes.
Upload the raw bytes to `upload.url` using the returned method and headers,
then call [Complete a file](api:POST/v1/files/{file_id}/complete) to mark the
file ready. Until the file is `ready`, you cannot attach it to an authorization.
File creation does not link the file to anything. Attach a `ready` file to an
authorization with
[Attach a file](api:POST/v1/prior-authorizations/{authorization_id}/attachments).
## Returns
Returns the pending file and a single-use upload target.