Compatibility with Symfony 5.4

Initial error is 

`Compile Error: Declaration of LdapTools\Bundle\LdapToolsBundle\DependencyInjection\Security\Factory\LdapFormLoginFactory::getKey() must be compatible with Symfony\Bundle\SecurityBundle\DependencyInjection\Security\Factory\FormLoginFactory::getKey(): string`

More errors may be found while working on this issue