post https://rls.congacloud.com/api/filestore/v1/files/multipart-uploads
Starts a multipart upload by creating an upload session.
It returns an upload ID for use in subsequent API calls to:
- Upload individual parts of the file (UploadPartAsync)
- Complete the multipart upload (CompleteMultipartUploadAsync)
- Abort the multipart upload if needed (AbortMultipartUploadAsync)
The multipart upload process allows to upload large files in smaller chunks,
providing better reliability for large file transfers and the ability to pause/resume uploads.