Refactor/remove everest_to_ert

[oyvindeide]

When everest needs to run the forward model, it first needs to create an ert config, as that is required for the BaseRunModel. However only a small subset of that config is actually used, while we still create the ert analysis config, etc.

Instead we should just create the parts that we actually require in the everest run model. This means refactoring the base run models to only take the configuration they actually need in the constructors.