Farmers markets across Massachusetts are being celebrated this week as the last days of August unfold. The week kicks off with the 27th annual Massachusetts Tomato Contest today at Boston’s City Hall Plaza. The state’s secretary of Energy and Environmental Affairs, Richard Sullivan, said farm markets are festive places to find fresh, locally grown products and also help keep agricultural traditions alive. Agriculture commissioner Scott Soares said there are 245 farm markets open in the state this summer, and many will continue indoors next winter. He says the number has more than doubled since 2005.