A drunken Rhode Island man drove a car through City Hall plaza last night and down three flights of stairs — “miraculously” missing pedestrians along the way — before slamming into a pole on nearby Congress Street, police said.Boston police said Nicholas Hoetzel, 26, of Tiverton, R.I., then jumped from the car and fled, only to be found unconscious on State Street with several “self-inflicted” wounds.