Bug 35450: Preservation system preferences should authval dropdowns

Bug 35450: Preservation system preferences should authval dropdowns

This patch updates two preservation module system preferences so that
they offer dropdowns of "Not for loan" values instead of requiring entry
of a specific code.

The patch also adds a missing "." at the end of one preference
description.

To test, apply the patch and restart services.

- Go to Administration -> System preferences.
- Search for "preservation"
- Check that the "PreservationNotForLoanDefaultTrainIn" and
  "PreservationNotForLoanWaitingListIn" preferences have dropdowns
  offering "Not for loan" values.
- Confirm that your choices are correctly saved.

Signed-off-by: Barbara Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 20d0d94f22aeab3c71d22b6a99fbfa4421e1f40d)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>