The Boston Celtics are heading into one of the most consequential offseasons in franchise history. Brad Stevens has made clear the front office will do everything in its power to put another championship-caliber roster together. The pieces are in place. The assets exist. The question is how aggressively Boston moves.One name keeps coming up above all others. Giannis Antetokounmpo is expected to be traded by the Milwaukee Bucks this offseason, an…