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/backups.nix

@@ -62,6 +62,7 @@ let
     ''}
     ${config.services.bitcoind.dataDir}
     ${config.services.clightning.dataDir}
+    ${config.services.clightning-rest.dataDir}
     ${config.services.lnd.dataDir}
     ${optionalString (!cfg.with-bulk-data) ''
       - ${config.services.liquidd.dataDir}/*/blocks