Saudi Arabia and its Persian Gulf allies are backing a formal partnership with a 10-nation group led by Russia to try to manage the global oil market, according to OPEC officials, in an alliance that would transform the cartel. The move, which some OPEC officials say would help put a floor on oil prices, comes as the cartel faces pressure from President Trump to keep prices low and as increased output from American shale producers reduces the influence that cartel members have over the market. …