Investigate redis AOF storage option

[ffissore]

From this flowdock came out the suggestion to use redis as a queue mechanism.

Redis offers a storage option called AOF that together with RSMQ could make it a nice queue system, with the speed of redis and the advantage of not complicating our infrastructure (which was one of the aspects of #2972 that received most criticism)

Our redis instance is run by amazon. Investigate

• if we can turn AOF on (or if it's on already)
• if queued messages are actually delivered after a redis restart (outage simulation)

[jviotti]

Our redis instance is run by amazon

Notice we run Redis in the k8s cluster on Amazon, but we don't use a managed Redis instance.