sg_dir.

    These structured messages will be sourced by both /etc/update.motd.d
    and APT UA-configured hooks. APT hook content will orginate from
    apt-hook/hook.cc

    Call apt-esm-hook to render final human-readable
    messages.

    :param cfg: UAConfig instance for this environment.
    z.Updating Ubuntu Pro messages for APT and MOTD.rW