[WIP][FEATURE] Observe changes through Extbase repositories

[Mabahe]

Follow up of PR #2035

TODOs:

• Tests
• complete strict_types
• ...

If you wanna test this patch, register your model in ext_localconf.php

$domainObjectObserverRegistry = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(
    \ApacheSolrForTypo3\Solr\IndexQueue\DomainObjectObserverRegistry::class
);
$domainObjectObserverRegistry->register(
    \GeorgRinger\News\Domain\Model\News::class
);

[WebsiteDeveloper]

@Mabahe we have an earlier version of this patch running. There Seems to be an issue with Custom Initializers. Because those do not get respected on Updates to the extbase object.

[christophlehmann]

Close in favor of #3843 ?