[BUGFIX] Make daterange filtering in EXT:belog work again

Use ISO dates and date time objects consistently.

Change-Id: I1095f6690a3b73217657cc2577ebdaf6d7ff5fc0
Releases: master, 8.7
Resolves: #82126
Reviewed-on: https://review.typo3.org/55037


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>