Bug 34333: Add Koha::Hold->cancellation_requested

Bug 34333: Add Koha::Hold->cancellation_requested

This patch adds a helper method for telling if a hold has cancellation
requests. To be used for embedding such information.

To test:
1. Apply this patch
2. Run:
   $ ktd --shell
  k$ prove t/db_dependent/Koha/Hold.t
=> SUCCESS: Tests pass, the new method is covered by tests.
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: Tomas Cohen Arazi <tomascohen@theke.io>