Bug 28254: Make PUT /holds/:hold_id/pickup_location honour x-koha-override

Bug 28254: Make PUT /holds/:hold_id/pickup_location honour x-koha-override

This patch adds a new parameter (x-koha-override header) to the route,
and makes the controller pass this information (override requested) when
the AllowHoldPolicyOverride syspref is set, to
Koha::Hold->set_pickup_location.

This way, under certain conditions, we can be sure the update wont'
fail.

To test:
1. Apply this patchset
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/holds.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>