AliyunOSS: Improve copy file performance for AliyunOSSFileSystemStore

Aliyun OSS will support shallow copy which means server will only copy metadata when copy object operation occurs. 

With shallow copy, we can use copyObject api instead of multi-part copy api if we do not change object storage type & encryption type & source object  is uploaded by Put / Multipart upload api.

We will try to use copyObject api, and check result. If shallow copy disabled for this object, then we will use multipart copy. So, I will remove fs.oss.multipart.upload.threshold configuration.