* Our current SFTP implementation uses a single channel to transfer data. Connections with a high latency cause very slow transfer. github.com/pkg/sftp allows transferring data using concurrent streams, which seems to solve the problem. In order to utilize the feature, the remote file must implement the WriteTo() or ReadFrom() and Stat() methods. I've moved the progress bar to relay the data from a local file, as we can still call Read() or Write() on it to update the progress.
This PR doesn't address the high CPU usage by github.com/pkg/sftp on low latency links.
Closes#20579
* Cleanup
* Fix fileTransferProgress
* Simplify interfaces
* Move helper to utils package
Add comments
* Added comments
* Change canceler implementation to return correct values from Read/Write
* Fix infinite recursive call in cancelWriter.
