By Doyinsola Oladipo NEW YORK (Reuters) – The world’s largest cruise ship is set for its maiden voyage on Saturday, but environmental groups are concerned that the liquefied natural gas-powered vessel – and other giant cruise liners to follow – will leak harmful methane into the atmosphere. Royal Caribbean International’s Icon of the Seas sets sail from Miami with capacity for 8,000 passengers across 20 decks, taking advantage of the surging popularity of cruises. The ship is built to run on liquefied natural gas (LNG), which burns more cleanly than traditional marine fuel but poses greater ri…