add ClimaLandSimulation struct

[imreddyTeja]

Purpose

closes #1182

Adds a struct ClimaLandSimulation for the full, integrated land model. This PR also extends the necessary Interfacer functions for a simulation type (get_field, update_field!, step!, etc).

This PR requires CliMA/ClimaLand.jl#1035 from ClimaLand, so it uses that branch in the experiments/ClimaEarth/ environment. That PR will need to be merged and a release of ClimaLand made before we can merge this PR.

To Do

• add get_field functions
• extend new get_field functions for other surface models
  • emissivity -> return 1
  • displacement height -> return 0
• add update_field! functions
• update Interfacer docs
  • Q: do we want to require these fields to be extended for all surface model simulations? Or just add fallbacks that do nothing?
• add method for add_coupler_fields!, following add coupler fields based on simulation types #1207
• add test for constructor

Current status 2/27

Constructor fails in update_aux! because snow tries to access p.drivers.thermal_state.