[VnV][telemac3d] Update bendrans example with better choices for a few keywords

- TREATMENT OF NEGATIVE DEPTHS = 2 (new default value since release 9.0) and
TIDAL FLATS = YES (default value) to improve mass conservation of water
- use of gradient conjugate + preconditioning 34 = 2*17 to solve PPE, more
efficient than GMRES for this example (very few iterations are needed)
- ACCURACY FOR PROPAGATION = 1.E-15 as easily solved (only 2 iterations needed)
- ACCURACY FOR PPE = 1.E-9 (less than 10 iterations needed)
- PRECONDITIONING FOR DIFFUSION OF K-EPSILON = 34 to improve efficiency
(turbulent variable)
- PRECONDITIONING FOR DIFFUSION OF VELOCITIES set to default
(not understood why 0 previously, no clear differences)