[VnV][telemac3d] Update solit example (more efficient options to solve systems)

- SOLVER FOR DIFFUSION OF VELOCITIES = 1 (conjugate gradient)
+ PRECONDITIONING FOR DIFFUSION OF VELOCITIES = 34 (= 2*17) rather than GMRES
- accuracy for propagation and diffusion of velocities = 1.E-15 easily reached
with previous choices
- ACCURACY FOR PPE set to 1.E-9