dev_cross: Fix the saving of probabilities, percentiles and metrics for seasonal and sub-seasonal cross-validation workflows

Hi @ptrascas,

This branch has the changes needed to save:

• The probability categories
• The requested percentiles for the observations
• RPSS and other metrics

I have also:

• Fixed a check in the recipe to allow requesting binary probablity categories (like [1/10] or [9/10])
• Added the fixed version of CST_MergeDims()

Could you please test it and let me know if everything works as expected for your operational case?

If you want to add these changes to your bigpredidata branch, you can merge or directly copy the modified functions there. If you need any help with this, please don't hesitate to let me know.

Thanks,

Victòria

FYI @nperez