Add biogeochemistry interface to ocean_simulation

[vtamsitt]

1. At minimum this requires adding a biogeochemistry kwarg to the ocean_simulation function (the BGC model can be initialised beforehand with the grid):

https://github.com/CliMA/ClimaOcean.jl/blob/514135fc9a1016ec0c32081fe3914e789b3d35ca/src/OceanSimulations/OceanSimulations.jl#L55-L68

3. A way to pass BGC boundary conditions (e.g. surface air-sea CO2 flux) and merge with existing ocean_boundary_conditions, and ideally also a way to pass through custom BGC forcings

4. Also I think the BGC tracers that are defined within the biogeochemistry model need to be added to tracers for tracer_advection? Could perhaps extract the tracers initialised in the BGC model using Oceananigans.Biogeochemistry.required_biogeochemical_tracers(biogeochemistry) and merge with existing tracers?

cc @glwagner @jagoosw