Bug 31264: Curbside pickups - Take CalendarFirstDayOfWeek into account

Bug 31264: Curbside pickups - Take CalendarFirstDayOfWeek into account

We need to take the pref CalendarFirstDayOfWeek into account to display
the days on the curbside pickups admin page.

Test plan:
Turn on the CurbsidePickup pref
Set CalendarFirstDayOfWeek to Sunday
Go to the curbside pickups admin page, add new slots, and confirm that
Sunday is displayed first.
Try again with CalendarFirstDayOfWeek set to Monday and Saturday.

Sponsored-by: Association KohaLa - https://koha-fr.org/
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>