add standalone clightning-rest service

- Rename `services.rtl.cl-rest` to `services.clightning-rest`.
  `clightning-rest` is generally useful for connecting external REST clients
  to clightning.

- Add a dedicated network namespace in netns-isolation.

- Add nodeinfo entry.

- Add datadir (which contains REST auth data) to backups.

modules/nodeinfo.nix

@@ -27,6 +27,7 @@ let
     lnd = mkInfo ''
       info["nodeid"] = shell("lncli getinfo | jq -r '.identity_pubkey'")
     '';
+    clightning-rest = mkInfo "";
     electrs = mkInfo "";
     spark-wallet = mkInfo "";
     btcpayserver = mkInfo "";