put method
put generic key value pairs
@param key String @param value Object @return traits RudderTraits
Implementation
RudderTraits put(String key, dynamic value) {
  if (key == "extras") {
    RudderLogger.logError(
        "extras is a reserved key. Please use any other key instead.");
    return this;
  }
  Map<String, dynamic> extras =
      __traitsMap.putIfAbsent("extras", () => <String, dynamic>{});
  extras[key] = value;
  return this;
}