Use into_bytes_stream and into_bytes_sink instead of io::copy

[Xuanwo]

          @Xuanwo  Does OpenDAL have a recommended way to copy an object between two services? Then I could switch to that approach after this PR. Using `futures::io::copy` requires `AsyncRead` and `AsyncWrite`.

Maybe using streams and sinks?
https://docs.rs/opendal/latest/opendal/struct.Reader.html#method.into_bytes_stream
https://docs.rs/opendal/latest/opendal/struct.Writer.html#method.into_bytes_sink

Originally posted by @evenyag in #4037 (comment)

[evenyag]

https://docs.rs/futures/latest/futures/stream/trait.StreamExt.html#method.forward
Then we can use forward to send contents to the sink.

[killme2008]

https://docs.rs/futures/latest/futures/stream/trait.StreamExt.html#method.forward Then we can use forward to send contents to the sink.

It seems a good idea, assign this task to you. It may relate to the write buffer and read cache etc.