Slugs of dates are generated during import.
This might lead to confusion if the time zone differs from frontend.
Therefore the time zone is now configurable to allow adjustments for the
actual website.
A new interface `TimeZoneProviderInterface` is provided which can be re
configured to a different implementation.
The default implementation will use TYPO3s `SYS.phpTimeZone` setting,
with fall back to `date_default_timezone_get()` call.
That way it should be useful for most systems out of the box.
Resolves: #11345
