Add a performance test

Hi @jorgensd, thanks for the huge work done for the FEniCSx. As one of the many users of FEniCS/FEniCSx, I really think at least two points of FEniCSx are attracting: (1) convenience for solving PDEs and (2) the high computational efficiency based on parallel computation. I think the first point is already well illustrated in this tutorial. However, it would be better to illustrate the computational efficiency of FEniCSx versus other software such as Matlab.