GRIB 2 output

[clechartre]

Purpose

This is the equivalent of DRAFT PR #42 now adapted to this repository (previously tailored to the MeteoSwsiss/neural-lam fork)
Outputting the inference results as GRIB format. Therefore, this needs the inference PR to be merged previously (loads of changes come from this).
This integrates the functionality of transforming the .npy array that is originally produced into a GRIB from a template.

Code changes:

• ar_model: add to the function on_predict_epoch_end a function generate_time_step to generate time steps markers for the grib files and a function that translates the npy output into a grib file.
• other modifications to the code include adaptation to tsa, imports of new libraries for this functionality, and references to templates in data_config.yaml

Checklist

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• You have followed the coding standards guidelines established at Code Review Checklist.
• Docstrings and type hints are added to new and updated routines, as appropriate
• All relevant documentation has been updated or added (e.g. README)

Review

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