Need to track age of flight contact events and remove after expiration

[autodidaddict]

The event sourcing system needs to keep track of when each contact event delivered from the provider occurred so that the cached state contains a value indicating how old that particular flight record is. After a flight (tracked via icao_address key) hasn't been heard from after some configurable value, like 5 minutes, the flight should be removed from the materialized state view.

To do the demo today, you need to run flushdb on the Redis database before running it because the system just accumulates more and more flights without ever reducing the list.