Upload a file attachment to a credentialing workflow

Uploads a file attachment to the credentialing workflow identified by workflowId using a multipart/form-data request. The form must include: id (the target record identifier), file (the binary file to upload), and expirationDate (optional —). The file is stored in cloud storage and the attachment metadata is saved on the workflow record. Requires the tenant-id header to scope the operation to the correct tenant.