(Adds details) By Padraic Halpin DUBLIN, Jan 25 (Reuters) - Ireland's Jonathan Sexton will join French side Racing Metro next season after the Irish Rugby Football Union (IRFU) said on Friday the flyhalf would not be renewing his contract with European champions Leinster. Sexton, who won three Heineken Cups in four seasons with Leinster and has become one of Ireland's most influential players, has been offered a two-year contract with the Paris-based side, a source close to the deal told Reuters.