New generic customizable retry mechanism, independent from GitHub

[marco-m-pix4d]

Best reviewed commit per commit:

• first we introduce the new retry package
• then we integrate it in cogito

Note that:

1. In the name of resilience, I changed the behavior in case of zero or negative sleep time: we do not try any more to be smart, we fall-back to the default back-off sequence. In particular, have a close look at the tests. I arrived at this approach after many attempts, but for sure I might have missed something, so we can change if needed.
2. To keep things simple and incremental, the new retry mechanism does not support jitter. I think this can be safely added back later.

Part of PCI-3309.