Fix climatology_bounds of the preprocess data

[SarahAlidoost]

In notebooks (after merging #38), we add seasons as time values together with climatology_bounds, like this example. The preprocessed data can be read with both iris and xarray. However, some operations might return an error, for example:

ds = xr.open_dataset("./AtlasData/preprocess/atlas_EUCP_CNRM_CMIP6_KCC_cons_tas.nc")
ds.to_array()

ValueError: coordinate climatology_bounds has dimensions ('climatology_bounds',), but these are not a subset of the DataArray dimensions ('variable', 'time', 'latitude', 'longitude', 'percentile')