Create and return the configuration with appropriate defaults.

def make_config(self, instance_relative: bool = False) -> Config:
        """Create and return the configuration with appropriate defaults."""
        config = self.config_class(
            self.instance_path if instance_relative else self.root_path,
            DEFAULT_CONFIG,
        )
        config['ENV'] = get_env()
        config['DEBUG'] = get_debug_flag()
        return config