[Round 2] Add option to set new metadata to with CopyObject

[mniewrzal]

By default metadata from original object is copied into new object but to be s3 compatible we need an option to set new metadata while creating a copy of the object. We need to:

• define where and how to put this option (most probably CopyObjectOptions.Metadata)
• integrate with server-side (we need to implement server-side first)

[storjBuildBot]

Change https://review.dev.storj.io/c/storj/uplink/+/6996 mentions this issue.