Add on-blur back-end partial validation

[ddahan]

Double validation is kind of cumbersome. Maybe we should think of get ride of front-end validation and use some tricks to have back-end validation only, while keeping a good UX.

• Replace by native html5
• OR back-end validation on-blur? For example thanks to Partial Validation Pydantic

[ddahan]

However, it's good to have both options for different use cases. Maybe we could keep the current front-end validation, and add another dedicated form with specific back-end validation.