nixos/borgmatic: default to the correct user when username is configured

    // {

      postgresql_databases = map (

        d:

        let

          as_user = if d ? username then "${pkgs.sudo}/bin/sudo -u ${d.username} " else "";

        in

        {

          pg_dump_command =

            if d.name == "all" then "${postgresql}/bin/pg_dumpall" else "${postgresql}/bin/pg_dump";

          pg_restore_command = "${postgresql}/bin/pg_restore";

          psql_command = "${postgresql}/bin/psql";

            if d.name == "all" then

              "${as_user}${postgresql}/bin/pg_dumpall"

            else

              "${as_user}${postgresql}/bin/pg_dump";

          pg_restore_command = "${as_user}${postgresql}/bin/pg_restore";

          psql_command = "${as_user}${postgresql}/bin/psql";

        }

        // d

      ) (s.postgresql_databases or [ ]);