Add env var to prevent down migrations decrypting tables, add encryption to CHANGELOG.md
Created by: arussellsaw
I realised that anyone with database access could just decrypt tables by setting apply_reverse = true on the table, @eseliger recommended a safety of an env var that must be set to enable this to happen.
https://sourcegraph.slack.com/archives/CHPC7UX16/p1618905663056700
i've also added to CHANGELOG