Retry package downloads with a delay

[gaborcsardi]

[gaborcsardi]

This is actually not as simple as it looks. We should probably not retry 404 and 401 and similar errors, because it is unlikely that those would work a minute later. Failing after an hour and 30 retries is much-much worse than failing after one try and one minute.

OTOH we could retry 5xx errors, maybe?

But we haven't seen issues with PPM for a while, so it is unclear if we still need this.