Bug 34365: Add cancellation request flow to DELETE /holds

Bug 34365: Add cancellation request flow to DELETE /holds

This patch adds a new `x-koha-override` header to allow enforcing the
cancellation request flow for waiting holds.

If the hold is not waiting, the header has no effect.

To test:
1. Apply the tests patch
2. Run:
   $ ktd --shell
  k$ prove t/db_dependent/api/v1/holds.t
=> FAIL: The endpoint doesn't implement the required logic
3. Apply this patch
4. Repeat 2
=> SUCCESS: Tests pass! The endpoint behavior is changed!
5. Sign off :-D

Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>