apply default postgres connection config from dotfiles and .pgpass

This solves two minor problems with pg's default connection parameters:

• it doesn't read ~/.pgpass/PGPASSFILE
• user defaults to the OS user. In our work we always use Docker and the postgres user, so we can configure that as the default with the following in package.json or .get-pg-configrc etc:

  "get-pg-config": {
    "defaults": {
      "user": "postgres"
    }
  }