761: Integrate deserr r=irevoire a=loiclec
1. `Setting<T>` now implements `DeserializeFromValue`
2. The settings now store ranking rules as strongly typed `Criterion` instead of `String`, since the validation of the ranking rules will be done on meilisearch's side from now on
Co-authored-by: Loïc Lecrenier <loic.lecrenier@me.com>