Bug 30023: Add Koha::Old::Checkout->anonymize

Bug 30023: Add Koha::Old::Checkout->anonymize

This patch adds the mentioned method. It replicates the Koha::Old::Hold
behavior, including the exception thrown on bad configuration.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Old/Checkout.t
=> SUCCESS: Test pass
3. Sign off :-D

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>