_oe_whitelabel_starter_event_preprocess_date disregards site timezone

[drishu]

$dates->get('start_date') and $dates->get('end_date') have timezone set to UTC, but the sites have Europe/Brussles (as per php timezone set on server) when installed.
The core formatter handles this by fetching the timezone, I think we should do the same, something like
\Drupal::config('system.date')->get('timezone.default') and also account for users timezone (will be null if not allowed or not set so we can check for that).
Steps to reproduce:

• install oe_whitelabel
• create an event, set start date with His 00:00:00 and end date with his 23:59:59
• visit /nodes
• you will see the start date 1 day earlier than set

The issue becomes bigger if we would display the hour (ex requirement for teaser on one of the subsites)