Fix isFeatureAllowed string comparison

This fixes michnhokn#20.
This also should fix michnhokn#19.

The [`str_contains` function works vice-versa](https://www.php.net/manual/en/function.str-contains.php) than implemented before. In a local test environment this fixed the issues above and worked fine again.

CookieBanner.php

@@ -29,7 +29,7 @@ public static function isFeatureAllowed(string $featureName): bool
         if (($cookie = self::getCookie()) === null) {
             return false;
         }
-        return str_contains($featureName, $cookie);
+        return str_contains($cookie, $featureName);
     }
 
     public static function allowedFeatures(): array