Add a key-value pair to the extra_data dict.

        This can be used to add attributes that are not available when
        ray.profile was called.

        Args:
            key: The attribute name.
            value: The attribute value.

def set_attribute(self, key, value):
        """Add a key-value pair to the extra_data dict.

        This can be used to add attributes that are not available when
        ray.profile was called.

        Args:
            key: The attribute name.
            value: The attribute value.
        """
        if not isinstance(key, str) or not isinstance(value, str):
            raise ValueError("The arguments 'key' and 'value' must both be "
                             "strings. Instead they are {} and {}.".format(
                                 key, value))
        self.extra_data[key] = value