A site has been chosen for the statue of Boston Celtics legend Bill Russell and the location will be announced today by Mayor Thomas M. Menino, a team spokeswoman said yesterday. The mayor will be joined by Celtics co-owner Stephen Pagliuca and members of the Bill Russell Legacy Project Committee in detailing plans for a tribute to the NBA Hall of Famer. In February, President Obama presented Russell, who won 11 NBA titles with the Celtics as a player and a coach, with the Presidential Medal of Freedom in honor of his civil rights advocacy.