rsync-like --remove-source-files option for sftp

[supRy]

https://github.com/blinksh/blink/issues/567#issuecomment-1149329978

This is essentially a verified move command. It copies files and once confirmed to be on the destination, it removes from the source. This provides much safer file moves across unstable network connections compared to alternatives such as a typical sftp copy, then manually removing files after complete, since it removes the human from the process and won't remove files which didn't fully copy due to a network interruption.

I understand you aren't going to port all of rsync, but I think this could be an option added to the existing sftp in Blink.

https://explainshell.com/explain?cmd=rsync%20--remove-source-files