NewGracefulContext will create a GracefulContext with an idle time which should be longer than a typical operation cadence, and a "force after" duration which should be long enough to let some amount of operations to finish.

NewOutbox creates a new Outbox with a MongoDB URI: `mongodb://hostname`.

Settings for how old different kind of unprocessed events needs to be to be processed by the periodic sweep.

Interval in which to do a sweep of various unprocessed events.

GracefulContext is a context that can be gracefully cancelled after the original context has been canceled, but with a grace period to let operations finish.

Outbox implements an eventhorizon.Outbox for MongoDB.