Native multipart copy

[gaul]

Presently S3Proxy emulates multipart copy with a range getBlob request followed by uploadPart. Instead jclouds should offer native support. Note that this will need the Azure part size workaround as the existing multipart upload code.

[gaul]

Azure does not support range copies:

https://docs.microsoft.com/en-us/rest/api/storageservices/fileservices/copy-blob

OpenStack does not document range copies:

https://developer.openstack.org/api-ref/object-storage/?expanded=copy-object-detail

Atmos and B2 do not support copies at all. Perhaps S3Proxy should just special case S3 to do native MPU copy?