make `ct upload-with-diff` work with multitrace resources

[alehander92]

usage:

ct upload-with-diff <multitrace-and-diff-data> # potentially Nikola can add more details here
# .. <codetracer replay-with-diff url>

# <multi..> is produced by `ct make-multitrace` : TODO fix issues
# where <set-of-traces> can be 
# <trace-archives-folder> or
# <single-trace-folder/id> [<other-trace-folder/id>*]

maybe we can have a shortcut for manual cases, combining record and upload, but this is bonus:

ct record --with-diff=last-commit --upload <myprogram>
# ..
# ct: ready: url: <codetracer-replay-with-diff-url> ; file: <local-file>