Bug 31948: Add timestamp to tmp_holdsqueue table

Bug 31948: Add timestamp to tmp_holdsqueue table

With the option to have real time updates to tmp_holdsqueue
a timestamp will be really helpful to help find the most recently
added entries.

To test:
* Place some holds on a record with available items
* Run build_holds-queue.pl
* Verify the hold shows up under circulation > holds queue
* Apply patch
* Run build_holds_queue.pl again
* Verify this works without any issues
* Turn on RealTimeHoldsQueue
* Update pick-up location, add another hold
* Make sure these changes are reflected in the holds queue as well
* Look at the database and verify timestamps are set

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>