Bug 24480: Fix insert_fields_ordered instead of append_fields in SimpleMARC

Bug 24480: Fix insert_fields_ordered instead of append_fields in SimpleMARC

Test plan :
 - create a marc modification template which add a new field to a record
 - apply that template to some records
 - verify that the new field is always appended at the bottom of the record, even if some fields are higher.
 - apply patch
 - apply template to another set of records
 - verify the added field is now ordered within the already existing fields in the records

Signed-off-by: Kelly <kelly@bywatersolutions.com>
Signed-off-by: Phil Ringnalda <phil@chetcolibrary.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>