[Round 2] Handle copying object to the same location

[mniewrzal]

One way to update metadata with S3 is doing server-side copy to the same location with new metadata. We should also support this case in uplink but we don't need to do full server-side copy operation but we can use UpdateObjectMetadata on uplink side when we detect that the source location is equal to the destination location.

AC:

• extend CopyObject method to handle coping to the same location
• use UpdateObjectMetadata metainfo endpoint to set new metadata if source location and destination location are the same and new metadata was set
• add test cases

[mniewrzal]

I just realized that we cannot use UpdateObjectMetadata directly as CopyObject needs to return object metadata. We have two solutions:

• adjust satellite to handle coping to the same location and return object metadata correctly
• just return error when user wants copy to the same location (we may do this initially and later go to first point)

[mniewrzal]

We need to implement that on server side first storj/storj#4604
After that we need to revisit if we need to do something for uplink too.