User registration: Enable extra field validation for user registration in Chamilo

[juancp-contidosdixitais]

This pull request introduces a new functionality to Chamilo that allows the use of a user extra field to validate user registrations. For instance, if we have an extra field to store passport numbers, we can ensure that there are no duplicate values.

This functionality also works on batch user registrations.

To utilize this functionality, you need to specify in "extra_fields_to_validate_on_user_registration" within configuration.php the extra fields you want to validate. For example:

$_configuration['extra_fields_to_validate_on_user_registration'] = [
'extra_fields' => [
'passport', 'employee_id'
]
];

[juancp-contidosdixitais]

Updated to add the same logic to the user add/edit actions from administration