A warn message should be logged when config size bigger than threshold * MAX_SIZE

[hainesc]

    def set_config(self, config):
        data = json.dumps(config)
        if len(data) > CONFIG_MAX_SIZE:
            raise PluginSDKException("config should not bigger than 1MB")
...

A warn log is appreciated when data size is bigger than, somewhat 0.8 * MAX_SIZE.