Support locale for date formating

[romaintailhurat]

Consider this VTL expression:

cast(cast("2000-" || MOIS_COLLECTE || "-01", date), string, "MMMM")

It currently always returns October but we would like to return the localized name instead (Octobre for a french locale).

Since we are using date-fns for that, it way be as simple as:

• get the browser locale (navigator.language ?),
• infer what to use for format here, by using the proper date-fns option.