nixos/mailman: add package option (#427455)

  cfg = config.services.mailman;

  inherit

    (pkgs.mailmanPackages.buildEnvs {

    (cfg.packageSet.buildEnvs {

      withHyperkitty = cfg.hyperkitty.enable;

      withLDAP = cfg.ldap.enable;

    })

        description = "Enable Mailman on this host. Requires an active MTA on the host (e.g. Postfix).";

      };

      packageSet = lib.mkPackageOption pkgs "mailmanPackages" { } // {

        type = lib.types.attrs;

      };

      ldap = {

        enable = lib.mkEnableOption "LDAP auth";

        serverUri = lib.mkOption {

      mailman.layout = "fhs";

      "paths.fhs" = {

        bin_dir = "${pkgs.mailmanPackages.mailman}/bin";

        bin_dir = "${cfg.packageSet.mailman}/bin";

        var_dir = "/var/lib/mailman";

        queue_dir = "$var_dir/queue";

        template_dir = "$var_dir/templates";