Create a document upload to provide Know Your Business (KYB) files for a business. This is a two-step flow:

1. Create Upload (this endpoint): Provide file metadata and receive a temporary upload_url.
2. PUT File: Upload the raw binary file contents to the returned upload_url with the Content-Type header matching file_type.

A maximum of 25 documents per business can be uploaded.

Uploading a file the business already holds — same file_name and file_size — is answered with
409 document_already_exists and the id of the document it is stored under. The file is kept as uploaded
the first time and does not count against the limit again, so a repeated upload is safe to ignore.

Example:

curl -X PUT \
     -H "Content-Type: $file_type" \
     --upload-file ./path/to/$file_name \
     "$upload_url"