NEWARK, N.J. — After an expensive legal fight, an ex-prosecutor who sued Gov. Chris Christie’s administration over his 2010 firing has been granted access by a judge to secret grand jury transcripts he says will help show he was terminated because he questioned the dropping of an indictment that involved a Christie donor who served on the governor’s transition team.The ruling by state Superior Court Judge Douglas Hurd, given to attorneys last week, is the latest chapter in a lengthy battle that has cost …