A group of hero ex-cops pulled a woman holding a 5-month-old baby from the East River on Sunday after the lady walked into the water carrying the child, the former officers told The Post. “We heard a lot of screaming, and somebody yelled, ‘You guys gotta get over there!’ ” said retired cop Kevin O’Donnell, who used to helm the Community Affairs Office at the NYPD’s 109th Precinct in Queens. “She was walking straight out into the water.” O’Donnell and pal Paul Pinsdorf, who served on the force