keycloak: Fix issue in authorization_url since python-keycloak 1.8.1

The scope and state query parameters in the authorization URL are now
handled by the KeycloakOpenID.auth_url method since the release of
python-keycloak 1.8.1.

To keep backward compatibility with older python-keycloak versions, like
the one used in production, while ensuring support for recent ones we need
to ensure scope and state query parameters will be overridden if provided
in extra_params dict.