Unclear error message on incorrect SoilPropertyPath

[BSchilperoort]

With an incorrect path to the soil property data, the following error will be raised. This is not very informative to the user.
Perhaps we should check for the validity of the provided paths? (e.g. if expected files exist).

Error message

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
File ~/venv/ecoextreml/lib/python3.8/site-packages/xarray/core/dataset.py:1317, in Dataset._construct_dataarray(self, name)
   1316 try:
-> 1317     variable = self._variables[name]
   1318 except KeyError:

KeyError: 'depth'

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
/home/bart/STEMMUS_SCOPE_Processing/notebooks/run_model_in_notebook_bart.ipynb Cell 10 in <cell line: 2>()
      [1](vscode-notebook-cell://wsl%2Bubuntu/home/bart/STEMMUS_SCOPE_Processing/notebooks/run_model_in_notebook_bart.ipynb#X12sdnNjb2RlLXJlbW90ZQ%3D%3D?line=0) # setup the model
----> [2](vscode-notebook-cell://wsl%2Bubuntu/home/bart/STEMMUS_SCOPE_Processing/notebooks/run_model_in_notebook_bart.ipynb#X12sdnNjb2RlLXJlbW90ZQ%3D%3D?line=1) config_path = model.setup(
      [3](vscode-notebook-cell://wsl%2Bubuntu/home/bart/STEMMUS_SCOPE_Processing/notebooks/run_model_in_notebook_bart.ipynb#X12sdnNjb2RlLXJlbW90ZQ%3D%3D?line=2)     ForcingFileName="ZA-Kru_2000-2002_FLUXNET2015_Met.nc",
      [4](vscode-notebook-cell://wsl%2Bubuntu/home/bart/STEMMUS_SCOPE_Processing/notebooks/run_model_in_notebook_bart.ipynb#X12sdnNjb2RlLXJlbW90ZQ%3D%3D?line=3)     NumberOfTimeSteps="10",
      [5](vscode-notebook-cell://wsl%2Bubuntu/home/bart/STEMMUS_SCOPE_Processing/notebooks/run_model_in_notebook_bart.ipynb#X12sdnNjb2RlLXJlbW90ZQ%3D%3D?line=4) )
      [6](vscode-notebook-cell://wsl%2Bubuntu/home/bart/STEMMUS_SCOPE_Processing/notebooks/run_model_in_notebook_bart.ipynb#X12sdnNjb2RlLXJlbW90ZQ%3D%3D?line=5) print(config_path)

File ~/STEMMUS_SCOPE_Processing/PyStemmusScope/stemmus_scope.py:84, in StemmusScope.setup(self, WorkDir, ForcingFileName, NumberOfTimeSteps)
     81 forcing_io.prepare_forcing(self._configs)
     83 # prepare soil data
---> 84 soil_io.prepare_soil_data(self._configs)
     86 # set matlab log dir
...
--> 175     raise KeyError(key)
    177 ref_name, var_name = split_key
    178 ref_var = variables[ref_name]

KeyError: 'depth'