By Andrew Chung (Reuters) -Boston violated the free speech rights of a Christian group by refusing to fly a flag bearing the image of a cross at City Hall as part of a program that let private groups use the flagpole while holding events in the plaza below, the U.S. Supreme Court unanimously ruled on Monday. The 9-0 decision, authored by liberal Justice Stephen Breyer, overturned a lower court’s ruling that the rejection of Camp Constitution and its director Harold Shurtleff did not violate their rights to freedom to speech under the U.S. Constitution’s First Amendment. President Joe Biden’s a…