ST. PETERSBURG, Fla. \- Leave it to the Rays to sign a proven commodity on the cheap. Tuesday’s signing of Amed Rosario to a one-year, $1.5-million deal, or little more than twice the MLB minimum of $740,000, provides manager Kevin Cash with a veteran right-handed bat, a little speed and, most important in the Rays Way of doing business, roster flexibility. True, Rosario’s .964 fielding percentage in 95 games (84 starts) at shortstop with the Guardians and Dodgers last season would have ranked only 19 given he had enough reps to qualify for MLB leadership. That being noted, the 28-year-old is …