Retry incremental upgrade downloads
Originally created by Tails on #5825 (Redmine)
Downloading target files should be more robust on flaky Internet connections.
E.g. when a target file download times out, it should be retried a few times. Ideally, the download should be resumed using the already downloaded partial content. Possible implentation ideas:
- LWP::UserAgent::ExponentialBackoff - not in Debian, not sure it resumes interrupted downloads)
- LWP::UserAgent::Determined - in Debian, not sure it resumes interrupted downloads)
- code samples that use the Range header when needed
Alternatively, there could be a button for manually retrying or resuming an interrupted download.
- Is duplicate of #15875