Bug 33684: Make mandatory date fields required when editing a patron

Bug 33684: Make mandatory date fields required when editing a patron

Date fields in BorrowerMandatoryField are not required by the validation
form when a new patron is added or modified.

This is because the 'required' prop does not exist on the input element
when the flatpickr instance is created.
We should either add it in the DOM directly (tt), but it will require to
do it "manually" for each date fields, or add it when we add it to the
inputs. This patch implements the second option.

Test plan:
1. Add "dateofbirth" to syspref BorrowerMandatoryField.
2. Add patron and leave date of birth input field empty.
3. Save.
=> Form is not submitted and you are asked to fill in a date of birth

Signed-off-by: Emmi Takkinen <emmi.takkinen@koha-suomi.fi>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
https://bugs.koha-community.org/show_bug.cgi?id=33648
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>