devkit-flash: Allow for configureable number of retries

The main purpose of this is to allow infinite retries.
The discussion on the community channel revealed that people will have connectivity problems. This solution is not perfect for unreliable connections, but it's better. Perhaps the ideal solution would be to leave the file between runs and let the user control when to download (data caps, offline periods, etc).
2 jobs for resume in 2 minutes and 3 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed build:deb #8063
librem5

00:01:34

passed build:docs #8062
librem5

00:02:03