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

Inspired by
- https://github.com/dandi/dandi-archive/issues/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 (https://github.com/con/duct/issues/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.