Implement exponential backoff on requeue

[brettscott]

Requeue is primarily used when a service is temporarily unavailable. Knowing the exact recovery time is difficult to know as it could be a very temporary network glitch or a DB timeout dude to congestion.

Previous implementations supported infinite retries (which can cause a self-inflicted DOS attack).

We need something in between a fixed-time window and infinite. A compromise could be an exponential backoff where the requeue TTL increases exponentially up to an upper limit.