Converting field(s) to & from CF-compliant `xarray.Dataset`

A common way to work with weather and climate datasets is of course the xarray library, so it would be nice to have a means to convert to and from an xarray.Dataset if it has sufficient and conformant-enough CF metadata and suitable structure, for which the xarray.decode_cf function may be able to assist on the xarray-side.

Ideally we can have a method for such a conversion and/or at least a recipe in the documentation showing how this can be done, for both a trivially-convertible case and for a case of a field and/or Dataset that needs some tweaks to get the right structure before the conversion can be made.

Note in #706 we considered and supported input of xarray arrays, so that helps towards this.

Inizia esaminando l’issue #706 e la documentazione collegata di xarray Dataset, weather-and-climate e decode_cf. Determina i metadati CF e la struttura necessari per la conversione in entrambe le direzioni, includendo un caso diretto e uno che richieda modifiche strutturali; il lavoro è completato quando il metodo di conversione o una procedura documentata copre entrambi i casi.