Reduced gravity at the free surface is set to 0.98 m s-2 in some examples

[gustavo-marques]

To allow the model to run using a large time step, some of test cases ( e.g., flow down-slope) have the reduced gravity at the free surface set to 0.98 m s-2 (GFS = 0.98 instead of 9.8). Although this might be desirable for certain tests, it can mislead users. Since most users tend to use one of MOM6-examples as their starting point, we should try to keep the parameters within these examples as close as possible to realistic values.