Nextcloud 31 compatibility and some code cleanup

[juliusknorr]

Follow up to #1041 as there were quite some parts missing which makes the app not work properly with upcomping Nextcloud 31

• getLogger is removed since chore!: Remove ILogger and its friends  nextcloud/server#47978, replacing with the public logger method that does the same thing
• Move away from \OC::$server as it is internal API, ideally the app should use dependency injection more, but for quick migration switching to \OCP\Server::get works
• Remove usage of logException which is no longer available, also no need to pass app to each log statement as when getting the logger in the app scope we already have that set
• Cleanup service registration in Application.php as these days services will be auto wired based on the class name
• Move AppConfig over to use constructor property promotion as a new feature of PHP 8.0 that allows less lines of code