Mark Zuckerberg’s desperate tour to limit damage to Facebook from its massive Cambridge Analytica scandal heads to Congress next week amid growing calls to regulate the social network and a Bay State senator’s demands for a “privacy bill of rights.”Sen. Edward J. Markey, who will question Zuckerberg when he appears Tuesday at a high-stakes hearing in front of the Senate Judiciary and Commerce committees, said it’s time for Congress to guarantee Americans the right to online privacy.