nixos/syncoid: allow interval to be list of strings (#344355)

    package = lib.mkPackageOption pkgs "sanoid" { };

    interval = lib.mkOption {

      type = lib.types.str;

      type = with lib.types; either str (listOf str);

      default = "hourly";

      example = "*-*-* *:15:00";

      description = ''

        Run syncoid at this interval. The default is to run hourly.

        The format is described in

        {manpage}`systemd.time(7)`.

        Must be in the format described in {manpage}`systemd.time(7)`.  This is

        equivalent to adding a corresponding timer unit with

        {option}`OnCalendar` set to the value given here.

        Set to an empty list to avoid starting syncoid automatically.

      '';

    };