Add SCM atmos + bucket experiment

[juliasloan25]

We currently only run global coupled atmosphere + bucket experiments. It would be good to also have and maintain the capability to run a single column model (SCM) with these two models. This process may shine a light on pieces of our coupling infrastructure that are hard-coded or rigid, and is a step towards coupling an SCM using more complex surface models (soil, full land, ocean, etc).

Part of #1032