Add coastal wall-stress (log-law) boundary model to Langmuir turbulence case

[Tjnea1996]

I’m reproducing the McWilliams et al. (1997) open-ocean Langmuir turbulence setup using the default Oceananigans example. I’d like to extend it to a coastal case with a finite depth (~15 m) and a bottom log-law wall stress.

Should I just supply FluxBoundaryCondition functions in the script (like τb_u, τb_v), or is there an internal API for defining new drag closures inside Oceananigans?

[glwagner]

Simple quadratic drag laws can be implemented without any source code implementation. For example, the tilted bottom boundary layer example does this: https://github.com/CliMA/Oceananigans.jl/blob/main/examples/tilted_bottom_boundary_layer.jl, and there is a discussion here: #3264

It could make sense to enshrine the quadratic drag law in source code at some point, but the relative ease of implementing it with provided tools means we haven't pursued it.