Update the Postgres client binaries (psql et al) to version 14.0. This is so they match the server version, and so that pg_amcheck is available, which was introduced in 14.0. This requires updating the base image to Ubuntu 21.04 at the same time because the Postgres repo doesn't support version 14.0 on Ubuntu 20.10.
Config
This directory contains configuration files for Danbooru.
To configure your Danbooru instance, copy danbooru_default_config.rb to danbooru_local_config.rb and edit it. See danbooru_default_config.rb for details.
The only file here that end users need to be concerned about is danbooru_default_config.rb. The rest of the files here are internal Rails-related configuration files that end users shouldn't need to edit.