Make json schema validation an optional feature

Update!
This got even easier with PHP 8.1! 🎉
https://www.geeksforgeeks.org/how-to-validate-json-in-php/

So we can remove that dependency and replace the code with the following, until we have PHP 8.3 as dependency.

    // @todo Remove this if, once we require PHP >=8.3
    if (function_exists('json_validate')) {
      return json_validate($json);
    }
    else {
      trigger_error('JSON was not validated, as the current PHP version < 8.3 doesn\'t support json_validate(). Assuming the JSON is correct.');
      return TRUE;
    }

Let's postpone this on 🌱 [META] Make Drupal 10/11 compatible with PHP 8.3 Active . No need to implement this, when no Drupal version currently supports PHP 8.3.