Is your feature request related to a problem? Please describe.
I use a private S3 as primary storage. When I upload a big file using webui or desktop sync client, this file is send by chunk. Each chunk is store on S3 and finaly nextcloud download all chunks, assemble them and upload the entire file to s3.

The webDAV steps:

• MKCOL request
• PUT request of 10 MBytes
• MOVE request to merge

Describe the solution you'd like
It would be great if the sending of each chunk could match an S3 multipart sending. So the final merge step would be useless and the upload more fast.

S3 steps corresponding to webdav steps:

• https://docs.ceph.com/docs/bobtail/radosgw/s3/objectops/#initiate-multi-part-upload
• https://docs.ceph.com/docs/bobtail/radosgw/s3/objectops/#multipart-upload-part
• https://docs.ceph.com/docs/bobtail/radosgw/s3/objectops/#complete-multipart-upload

Describe alternatives you've considered
Pay beers to nextcloud developpers?

Additional context
no