The upstream haugene/transmission-openvpn v5.4.0 image uses systemd-resolved
via D-Bus in its update-resolv-conf script, which fails in HA containers
that lack systemd/D-Bus with 'sd_bus_open_system: No such file or directory'.
This adds a custom update-resolv-conf script that directly modifies
/etc/resolv.conf by parsing OpenVPN's foreign_option_* environment variables.
Co-authored-by: alexbelgium <44178713+alexbelgium@users.noreply.github.com>