Use 1D kernel to compute coarse-grained Richardson number profile

[ali-ramadhan]

See: https://github.com/CliMA/LESbrary.jl/pull/113#pullrequestreview-668547689

[glwagner]

Until we have support for this in Oceananigans it probably makes sense just to work with arrays. This is also easily computed in post processing, so we could speed up the simulation a bit by not calculating it online.