BOSTON — A Boston police officer who was shot in the face and critically injured when he approached a driver who was stopped during a gunfire investigation has been released from the hospital. Officer John Moynihan has returned home to continue rehabilitation and “the road to recovery promises to be challenging,” the police department said in a statement Saturday on its website. Moynihan, 34, was shot with a .357 Magnum on March 27 when police were responding to a report of gunfire in the city’s Roxbury neighborhood.