Add _csrf_confirm_form_route option for to the user/logout route

Problem/Motivation

This is a followup issue to https://www.drupal.org/project/openid_connect/issues/3508791 🐛 Add CSRF protection for /user/logout Active .

In that issue, we added CSRF protection to the logout link provided by OpenID Connect. The next step is to add a confirmation form to the route to follow the Core best practices (see: https://www.drupal.org/node/3152693 → ).

Steps to reproduce

1. Login with an OpenID provider.
2. Browse to `user/logout`
3. Currently receive a 403 access denied (because of the missing CSRF token).

Proposed resolution

Add the `_csrf_confirm_form_route` token to the logout route and provide the confirmation form to allow the logout action without the csrf token in the route.

Remaining tasks

[ ] Add the route option
[ ] Add the confirmation form
[ ] Add testing.