Get a random HTTP content type.

        :return: Content type.

        :Example:
            Content-Type: application/json

def content_type(self, mime_type: Optional[MimeType] = None) -> str:
        """Get a random HTTP content type.

        :return: Content type.

        :Example:
            Content-Type: application/json
        """
        fmt = self.__file.mime_type(type_=mime_type)
        return 'Content-Type: {}'.format(fmt)