To understand how important USA Baseball’s National High School Invitational, which kicks off for the fifth time on Wednesday, has become, perhaps looking at the Atlanta Braves’ farm system would suffice. Five of the Braves’ top 20 prospects participated in the national team event held each March — Kolby Allard would have been six had he not been hurt a year ago. To a man, they talk about the experience of the four-day tournament fondly.