(Refiles as UPDATE 7, not 6, text unchanged) By Elizabeth Piper, Andrew MacAskill and Muvija M LONDON (Reuters) – Liz Truss said on Thursday she would resign as British prime minister, brought down just six weeks into the job by an economic programme that roiled financial markets, pushed up living costs for voters and enraged much of her own party. The Conservative Party, which holds a big majority in parliament and need not call a nationwide election for another two years, will elect a new leader by Oct. 28. That contest is likely to pit ex-finance minister Rishi Sunak against Penny Mordaunt,…