See `mod` statements in postgres logs despite graphile-worker

[bickelj]

From #112: how do we get PostgreSQL mod logs but exclude a couple of annoying, frequent update statements that one of our libraries frequently runs?

I suppose there are two parts to this:

1. Can we enable log_statement = 'mod' in Digital Ocean's PG-as-a-service? If so,
2. how can we filter out frequent but inconsequential log statements?

See also PhilanthropyDataCommons/service#1266 which is to mitigate on the library side.