Add "staggered"/gradual interruption for upload (and possibly download)

[yarikoptic]

Inspired by

• Unembargo process results in error due to incomplete uploads dandi-archive#2021

and in particular the fact that we do not have yet user-accessible API to cancel interrupted/incomplete uploads. To minimize a number of such uploads, I think we should adopt approach similar to the one in offlineimap, and recommended by me also to con-duct (con/duct#184) to react to Ctrl-C so that we

• unless Ctrl-C is pressed 3 times consecutive within e.g. 3 seconds, we "de-queue" any uploads or downloads which are not yet completed, but otherwise continue until already ongoing processes continue to completion.