NumericFilter, allow to skip NULL values

[ceponcet]

Currently, NumericFilter Request displays NULL values.

Addition of a skipNullValues method, default false, to prevent querying null values.

    public function configureFilters(Filters $filters): Filters
    {
        $filters = $filters
           ->add(NumericFilter::new("age","fiche.filter.age")->skipNullValues(true));
        return $filters;
    }