Bug 30687: Allow pickup location to be forced when override is allowed

Bug 30687: Allow pickup location to be forced when override is allowed

This is Julian's patch with some extra cleanup to reduce repeated code

If AllowHoldPolicyOverride is enabled and only some pickup locations are
available, you still have the possibility to force one of the others
pickup locations.
But when there are zero pickup locations available, that is not
possible.

This patch change that by always displaying the list of pickup locations
when AllowHoldPolicyOverride is enabled.

Test plan:
1. Apply patch
2. Disable AllowHoldPolicyOverride
3. Create a biblio B with an item I at library A.
4. Configure this library A to not be a pickup location
5. Add a "Default holds policy by item type" for item I type where "Hold
   pickup library match" is "item's home library"
6. Try to place a hold on biblio B
   You should not be able to place a hold because there is no valid
   pickup locations
7. Enable AllowHoldPolicyOverride
8. Try to place a hold on biblio B
   You should now see all valid pickup locations in a dropdown list
   (with an exclamation mark in front of each option) with none selected
   by default
9. Verify you can place a title-level hold and an item-level hold

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>