Update to use more recent version of PostgreSQL

AWS has dropped support for PostgrSQL v10, and will force migrate folks to PostgreSQL v14 after 2023-04-17. We don't want to risk any issues.

Currently, the code is deployed against v10 in production, but is [tested with v11](https://github.com/mozilla-services/autograph/blob/7.1.6/database/Dockerfile#L1) with `make integration-test`, which is part of CI pipeline.