clightning: add cli option

An executable is more robust to use than shell aliases.

This is also a preparation for commit 'add module test' because the
NixOS testing framework makes interactive aliases hard to use: It
unsets 'PS1' which is used by programs/bash/bash.nix to detect
interactive shells.

modules/nix-bitcoin-webindex.nix

@@ -74,7 +74,12 @@ in {
       description = "Get node info";
       wantedBy = [ "multi-user.target" ];
       after = [ "nodeinfo.service" ];
-      path  = with pkgs; [ nix-bitcoin.nodeinfo nix-bitcoin.clightning jq sudo ];
+      path  = with pkgs; [
+        nix-bitcoin.nodeinfo
+        config.services.clightning.cli
+        jq
+        sudo
+      ];
       serviceConfig = {
         ExecStart="${pkgs.bash}/bin/bash ${createWebIndex}";
         User = "root";