Addition of bathymetry modification utilities

[GodotMisogi]

This merges the following changes:

1. A keyword argument for the timestepper used to evolve the sea-ice dynamics is added (5b5e631)
2. The functionality to modify a bathymetry is added with the function modify_bathymetry_depth! using kernels, intended for bathymetries processed through regrid_bathymetry. Tests have also been added in test_bathymetry.jl.

[glwagner]

Hi @GodotMisogi development of these utilities is now being done on NumericalEarth (eventually, via #757, these utilities will be ported into ClimaOcean from NumericalEarth as well). Can you open this contribution against NumericalEarth?