message: Allow calling config_value::set with C strings
diff: @@ -305,6 +305,8 @@ private:
  data_ = std::move(x);
  } else if constexpr (std::is_integral<T>::value) {
  data_ = static_cast<int64_t>(x);
  + } else if constexpr (std::is_convertible<T, const char*>::value) {
  + data_ = std::string{x};
  } else {
  static_assert(detail::is_iterable<T>::value);
  using value_type = typename T::value_type;
  