A former U.S. ambassador arrested at the beginning of December on charges of being a longtime secret agent for Cuba has agreed to be detained while he awaits trial rather than fight prosecutors who want him held in a federal lockup because they say he’s a flight risk. Victor Manuel Rocha, 73, who was indicted by a grand jury on Dec. 5, also asked a judge to postpone his arraignment until Feb. 16 to enter a plea in Miami federal court — a long gap for a routine proceeding that suggests he might be cutting a deal with prosecutors. Rocha’s defense attorney, Jacqueline Arango, filed a motion Frida…