Set auto password hasher for all user classes (see #6289)

Description
-----------

In Symfony 5.3 this config was added to the default security config in order to enable the `auto` password hasher for all user classes that implement this interface (see symfony/recipes#981) - which `Contao\User` also implements.

I think we should do the same in the `contao/managed-edition`. This way you don't have to define this yourself in case you are using HTTP Basic Authentication for some controller outside Contao's own firewalls. For instance, in [this example](contao/contao#6220 (comment)) the line

```php
$extensionConfig['password_hashers'][InMemoryUser::class] = 'auto';
```

could be omitted then.

Commits
-------

84c6d47a set auto password hasher to auto for all
ab0a6719 also set password hasher for Contao\User specifically
593d2448 update README and test config

Author: fritzmg

README.md

@@ -66,6 +66,7 @@ sections:
 security:
     password_hashers:
         Contao\User: auto
+        Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface: auto
 
     providers:
         contao.security.backend_user_provider:

tests/Functional/app/config/security.yaml

@@ -1,6 +1,7 @@
 security:
     password_hashers:
         Contao\User: auto
+        Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface: auto
 
     providers:
         contao.security.backend_user_provider: