show more details for "Hash Sum mismatch" errors

show more details for "Hash Sum mismatch" errors

Users tend to report these errors with just this error message… not very
actionable and hard to figure out if this is a temporary or 'permanent'
mirror-sync issue or even the occasional apt bug.

Showing the involved hashsums and modification times should help in
triaging these kind of bugs – and eventually we will have less of them
via by-hash.

The subheaders aren't marked for translation for now as they are
technical glibberish and probably easier to deal with if not translated.
After all, our iconic "Hash Sum mismatch" is translated at least.

These additions were proposed in #817240 by Peter Palfrader.