By Christoph Steitz and Nina Chestney FRANKFURT/LONDON (Reuters) -Russia resumed pumping gas via its biggest pipeline to Europe on Thursday after a 10-day outage, allaying some of Europe’s immediate supply fears but not enough to end the threat of rationing to cope with potential winter shortages. Supplies via Nord Stream 1, which runs under the Baltic Sea to Germany, were halted for maintenance on July 11 but, even before that outage, flows had been cut to 40% of the pipeline’s capacity in a dispute sparked by Russia’s invasion of Ukraine. Thursday’s flows were back at that 40% capacity level…