New endpoints

Introduced three endpoints to support multipart upload (uploading single files in multiple parts):

• POST /v3/multipart-uploads – Create pre-signed URLs for multipart upload of large files.
• GET /v3/multipart-uploads/{id}/status – Retrieve the current status of a multipart upload.
• POST /v3/multipart-uploads/{id}/complete – Initiate completion of a multipart upload after all parts have been uploaded.