Important: #108557 - Drop PageDoktypeRegistry onlyAllowedTables option 

Description 

It is possible to limit which tables are allowed for page types (doktype). However, up until now the default behavior when switching types was to ignore violations of these rules. The behavior could be changed for a particular doktype like this:

use TYPO3\CMS\Core\DataHandling\PageDoktypeRegistry;
use TYPO3\CMS\Core\Utility\GeneralUtility;

$dokTypeRegistry = GeneralUtility::makeInstance(PageDoktypeRegistry::class);
$dokTypeRegistry->add(
    116,
    [
        'onlyAllowedTables' => true,
    ],
);

This made page type 116 strict when switching the page type.

This option is now obsolete, as this functionality is always enabled. Switching page types is no longer possible if it violates the configured allowed tables, which makes the system more consistent.

Some remarks: This option was rarely used and often misunderstood. The option to configure allowed tables was called allowedTables. It was not clear what onlyAllowedTables meant without looking in the documentation.

From a practical point of view, it does not make sense to configure restrictions for page types when they are ignored by default for the action of switching types. Allowing the rules to be violated makes them ineffective in the first place. So either remove those restrictions altogether or make them always apply, which is what happens now.