A 19-year-old man from Medfield has been indicted in connection with a boat crash in Dennis that left a teen dead, according to officials. The Cape & Islands District Attorney’s Office announced that David K. Sullivan was indicted by a grand jury for his role in the death of 17-year-old Sadie Mauro. Mauro, a rising senior at Dover-Sherborn High School, was aboard a boat with several others when it crashed into a jetty in Sesuit Harbor around 9 p…