Put low res topography options in a config file

This is much less confusing than having them hard-coded deep inside of
global ocean.

Author: xylar

compass/ocean/mesh/low_res_topography.cfg

@@ -0,0 +1,16 @@
+# config options related to remapping topography to an MPAS-Ocean mesh
+[remap_topography]
+
+# the name of the topography file in the bathymetry database
+topo_filename = BedMachineAntarctica_v2_and_GEBCO_2022_0.05_degree_20220729.nc
+
+# variable names in topo_filename
+bathy_frac_var = ocean_mask
+
+# the description to include in metadata
+description = Bathymetry is from GEBCO 2022, combined with BedMachine
+              Antarctica v2 around Antarctica.
+
+# the target and minimum number of MPI tasks to use in remapping
+ntasks = 64
+min_tasks = 4

compass/ocean/tests/global_ocean/mesh/__init__.py

@@ -137,20 +137,14 @@ def configure(self, config=None):
         if config is None:
             config = self.config
         config.add_from_package('compass.mesh', 'mesh.cfg', exception=True)
-        # a description of the bathymetry
         if 'remap_topography' in self.steps:
             config.add_from_package('compass.ocean.mesh',
                                     'remap_topography.cfg', exception=True)
 
-        if not self.high_res_topography:
-            filename = 'BedMachineAntarctica_v2_and_GEBCO_2022_0.05_degree_20220729.nc'  # noqa: E501
-            description = 'Bathymetry is from GEBCO 2022, combined with ' \
-                          'BedMachine Antarctica v2 around Antarctica.'
-            config.set('remap_topography', 'topo_filename', filename)
-            config.set('remap_topography', 'bathy_frac_var', 'ocean_mask')
-            config.set('remap_topography', 'description', description)
-            config.set('remap_topography', 'ntasks', '64')
-            config.set('remap_topography', 'min_tasks', '4')
+            if not self.high_res_topography:
+                config.add_from_package('compass.ocean.mesh',
+                                        'low_res_topography.cfg',
+                                        exception=True)
 
         if self.mesh_name.startswith('Kuroshio'):
             # add the config options for all kuroshio meshes