Creates a presigned upload URL that allows uploading a file directly to storage, bypassing the need to send file bytes through the API.

Benefits over multipart upload:

• Reliability: File bytes are uploaded directly to storage, avoiding timeouts and connection resets that can occur when proxying large files through the API.
• Compatibility: Avoids issues with firewalls or proxies that block or scan multipart payloads containing binary content.
• Simplicity: The follow-up call to, e.g., candidate.uploadResume, candidate.uploadFile, or applicationForm.submit is a plain application/json request rather than multipart/form-data.

Requires the candidatesWrite permission.

Usage flow:

1. Call file.createFileUploadHandle with the file metadata to get a presigned upload URL, form fields, and a handle.
2. Upload the file directly to the returned url using a multipart/form-data POST request. Include all returned fields as form fields, and the file as the last field named file.
3. Use the returned handle in a follow-up call:
   • candidate.uploadResume with { candidateId, resumeHandle } to attach a resume to a candidate.
   • candidate.uploadFile with { candidateId, fileHandle } to attach a file to a candidate.
   • applicationForm.submit with Content-Type: application/json, where file field values in fieldSubmissions contain the handle string instead of a multipart file reference.

The presigned URL expires after 10 minutes. The fileUploadContext must be one of CandidateResume, CandidateFiles, or ApplicationForm.