NEW DELHI — Some of the hostages rescued from the weekend attack on an upscale restaurant in Bangladesh’s capital were questioned Monday by investigators searching for clues about the possible masterminds behind the gruesome attack that left 28 dead, including many foreigners. Authorities were still holding five of the 13 hostages rescued when commandos stormed the restaurant in Dhaka’s diplomatic zone Saturday morning, killing six of the attackers and capturing one, according to officials. Bangladesh police chief A.K.M.