OSLO, July 3 (Reuters) - A planned strike next week by Norwegian energy sector workers could cut the country's gas output by 292,000 barrels of oil equivalent per day, or 13% of output, employers' group the Norwegian Oil and Gas Association (NOG) said on Sunday. Oil output could be cut by 130,000 barrels per day, NOG added, corresponding to around 6.5% of Norway's production, according to a Reuters calculation. The strike, in which workers are demanding wage hikes to compensate for rising inflation, comes at a time of high oil and gas prices, with supplies of natural gas to Europe...