The morning sunlight is so bright in StepStone Group’s new office that the blinds are lowered. Situated on the top floor of One Haddington Buildings, the building, which runs parallel to the Grand Canal, commands views of St Mary’s Church and the popular 51 Bar.  Marcel Schindler, the head of private debt with StepStone, has flown in from Zurich for the formal opening of its new office this week. A tall, 21-year veteran with the firm, his division alone has capital responsibility for $70 billion in debt, in a firm which traces its roots in Ireland back 20 years. StepStone…