Better method for managing python black package

We are able to call `black` by shelling out to it on the system path, and we are able to cache its results by enforcing a version check on the binary. However, if it isn't on the path, or the version is wrong, we just show a helpful error message and let the user figure it out from there:

https://github.com/diffplug/spotless/blob/608e128381c89260f8a38fba985415c1f962ec7b/lib/src/main/java/com/diffplug/spotless/python/BlackStep.java#L65-L66

It would be nice if we could handle this better, or at least have better instructions. There are a few python plugins in the gradle ecosystem, I'll reach out to them to see if they are interested.

Commencez par BlackStep.java aux lignes indiquées par le lien afin de comprendre la recherche actuelle du chemin système, la vérification de version et le message d’erreur. Examinez les Gradle Python plugins mentionnés avant de choisir une approche ; le travail est considéré comme terminé lorsque les installations de Black manquantes ou incompatibles sont mieux prises en charge ou disposent d’instructions plus claires.

Rédigé par le modèle d'indexation à partir du texte de l'issue.