SOUTH PORTLAND — The city borrowed $12.7 million at 2.05 percent interest on Tuesday through a municipal bond sale that will finance the ongoing construction of a new municipal services facility on Highland Avenue, said Finance Director Greg L’Heureux. The city secured the low rate for a 20-year term after Standard & Poors and Moody’s Investors Service this month reaffirmed South Portland’s stable triple-A bond rating.