wire in the snowfall

[simone-silvestri]

with the new ClimaOcean (0.10) we also have a snow model attached to the sea ice by default.
This PR wires in the snow model

• the top temperature we solve for is the snow temperature
• the resistance for temperature computation is the resistance in series $\kappa^{snow} / h^{snow} + \kappa^{ice} / h^{ice}$
• we reroute the snowfall to increase the snow layer above sea ice