Bug 30692: Fix progress for ES indexing tasks

Bug 30692: Fix progress for ES indexing tasks

This patch makes the ES indexing task record progress properly.

To test:
1. Have ES setup
2. Edit a record making any change that would trigger indexing
3. Go to Administration > Background jobs
=> FAIL: The task status is 'Finished' but progress shows '0/1'.
4. Apply this patch
5. Restart the default worker:
   $ koha-worker --restart kohadev
6. Repeat 2 and 3
=> SUCCESS: Things work the same, but progress is '1/1'
7. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>