San Francisco Lyric Opera is making a substantial contribution to the Bay Areas holiday festivities. Their new production of Rossinis La Cenerentola is a small miracle. Established in their recently acquired home in the charming Florence Gould Theater at the Legion of Honor, with a small orchestra to replace the chamber ensemble of the old days, the company has mounted a show that is truly entertaining and vocally exciting, in spite of some flaws. It brought this listener more pleasure than some of this years offerings at the War Memorial Opera House. La Cenerentola opened on December 3 and has repeat performances scheduled for the evenings of December 4 and 10 and the afternoon of December 12.