[FEATURE] Queue initialization: Show number of queue items

Show the current number of queue items for the current
configuration.

Change-Id: Ie7c447f56ba66bb6a9a0bf164d63a4576d503486
Resolves: #43987
Reviewed-on: https://review.typo3.org/24990
Reviewed-by: Hans Höchtl
Tested-by: Hans Höchtl