Add support for S3 transfer manager callbacks (progress listeners)

[bunjiboys]

Is your feature request related to a problem? Please describe. With the non-Golang SDK's the S3 manager package supports providing a callback function to get information about data being sent to the S3 API, making it a lot easier to reliably track transfer speeds. Currently with the Go SDK, the only option is to wrap the writer/reader API's to do calculation based purely on local speeds.

Describe the solution you'd like Similarly to the Python and Node/JavaScript API's, add support for either a callback function or provide a channel that can receive the number of bytes transferred as each part is uploaded.

Describe alternatives you've considered As described above, I currently have a workaround wrapping the reader API for files to roughly track speeds, using the io.Writer* and io.Reader interfaces. However, this only tells you the speed of your local disks, and not the actual network transfers.

[lucix-aws]

This is referred to as "progress listeners" in the modern transfer manager specification, it's definitely something we intend to support in the next iteration of the feature.