put_multipart_chunk should NOT consume the chunk parameter

[szguoxz]

pub async fn put_multipart_chunk(
&self,
chunk: vec,
path: &str,
part_number: u32,
upload_id: &str,
content_type: &str,
) -> Result<Part, S3Error>

parameter chunk really should be of type &[u8] instead of a vec.
This makes a big difference as if my part is 100MB, you will require 100MB more memory. use &[u8] will allow me to reuse the read buffer.

[urkle]

Duplicate of #351