A top NYPD official on Wednesday blasted the group of migrants accused of pummelling a pair of cops in a caught-on-camera Midtown attack, calling the eight assailants “cowards” who “should be sitting on Rikers Island.” Four of the five young men taken into custody for the Saturday night brawl outside a migrant shelter on W. 42nd St. near Seventh Ave. were released without bail — enflaming the already heated debate surrounding the city’s migrant crisis. “You saw the video. Reprehensible,” NYPD Chief of Patrol John Chell told reporters following the annual State of the NYPD Breakfast at Cipriani…