Upgrade Redis OSS clusters on AWS

[duckduckgrayduck]

We'll start accruing charges starting February 1st if we don't

[allanlasser]

Lambdas pass data between themselves using Redis as an intermediate datastore. We believe Redis OSS changed owners, and may be branded differently.

[duckduckgrayduck]

Redis has been upgraded on staging and production to 6.0.5, which means we don't need to upgrade again until January of next year.