django/backends: Handle error when user session is no longer active
When a user session has been terminated without using the logout view (for instance a user can logout from all its authenticated sessions using the Keycloak account UI), the expired OIDC profile is still in webapp cache which causes errors and prevent new user logins.
So ensure to remove expired profile from cache when detecting Keycloak session is no longer active in django authentication backend.
Related to swh-web#3496 (closed)
Migrated from D6122 (view on Phabricator)