Before this change when the context was cancelled (due to
--max-duration for example) this could deadlock when uploading
multipart uploads.
This change fixes the problem by introducing another go routine to
monitor the context and close the pipe with an error when the context
errors.
This change checks the context whenever rclone might retry, and
doesn't retry if the current context has an error.
This fixes the pathological behaviour of `--max-duration` refusing to
exit because all the context deadline exceeded errors were being
retried.
This unfortunately meant changing the shouldRetry logic in every
backend and doing a lot of context propagation.
See: https://forum.rclone.org/t/add-flag-to-exit-immediately-when-max-duration-reached/22723
