Adapt probtest workflow to LETKF outputs

[cghielmini]

This merge request aims to adapt the protest workflow to LETKF outputs.

[clairemerker]

Thanks a lot for this PR! :)
I have a broader question regarding the logic we are trying to implement for fof_compare, please have a look at https://github.com/MeteoSwiss/probtest/pull/83/changes#r2676392953 before looking at my other comments. Maybe we can discuss, I am not sure I am remembering what we decided correctly, and I might be confused here...

[huppd]

Thanks a lot for these improvements and alignment with the other workflow. I just reviewed roughly the technical aspects and only have a few suggestions.

[cghielmini]

Thanks for your review:)

[cghielmini]

Thanks for your comment. It was a test related to the old version of probtest. We don't need it anymore, so I deleted it.

[clairemerker]

Thanks @huppd for the comments and @cghielmini for the improvements :)