Add bathymetry smoothing to global ocean init

We perform 6 iterations of smoothing with a weight of 0.9.

For more info on the smoothing approach, see:
MPAS-Dev/MPAS-Model#440
For more on previously chosen values (related to ice-shelf
cavities), see:
MPAS-Dev/MPAS-Model#532 (comment)

compass/ocean/tests/global_ocean/init/namelist.init

@@ -63,3 +63,5 @@ config_global_ocean_depth_conversion_factor = 1.0
 config_global_ocean_minimum_depth = 10
 config_global_ocean_deepen_critical_passages = .false.
 config_block_decomp_file_prefix = 'graph.info.part.'
+config_global_ocean_topography_smooth_iterations = 6
+config_global_ocean_topography_smooth_weight = 0.9