McKINNEY, Texas — Texas Attorney General Ken Paxton had an investment opportunity: a tech startup making data servers. He told people he had put his own money into Servergy Inc., according to prosecutors, and helped persuade a state lawmaker and another wealthy businessman to buy more than $100,000 in shares.All the while, Paxton was actually being compensated by Servergy, according to an indictment unsealed Monday, the same day the state’s top law enforcement officer turned himself in to jail on securities …