update an etcd key value pair

etcdservice.dart

setEtcdValue(ConfigData data) {
  var key = utf8.encode(data.name);
  var value = utf8.encode(data.value);
  String _body =
      "{\"key\": \"${base64.encode(key)}\", \"value\":\"${base64.encode(value)}\"}";
  print(_body);
  http.post("http://localhost:2379/v3/kv/put", body: _body);
}