Support x-amz-metadata-directive in CopyObject

https://docs.aws.amazon.com/AmazonS3/latest/API/API_CopyObject.html#API_CopyObject_RequestSyntax

Need to support x-amz-metadata-directive: specifies whether the metadata is copied from the source object or replaced with metadata that's provided in the request. When copying an object, you can preserve all metadata (the default) or specify new metadata. If this header isn’t specified, COPY is the default behavior.

Valid Values: COPY | REPLACE