Add Event-based metrics#127

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Oisin-M wants to merge 3 commits intodevelopfrom

Commits on May 7, 2024

add some vtb functions - not working at the moment
corentincarton
committed

Commits on May 17, 2024

Events update. Implement StdevEvent. And some more.
martin-janousek-ecmwf
committed

Commits on May 24, 2024

Implement quantile-type event classes. Cleaning of unused methods. Still not sure if the API is correct, pending the implementation of probability_quantiles methods.
martin-janousek-ecmwf
committed