Create a presigned upload URL for a CSP financial document.

Prerequisites: The business must have an accepted CSP offer and an active CSP funding that has not been paid out yet. Document uploads are no longer possible once the submission has been finalized.

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 20 documents per business can be uploaded.

Example:

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

Example flow:

1. Fetch the current state via List CSP Financial Documents to check if a submission is already in progress or pick up where a previous session left off.
2. Upload one or more documents using this endpoint.
3. Optionally remove unwanted documents via Delete CSP Financial Document.
4. Once at least one document is uploaded, finalize via Finalize CSP Financial Documents Submission.