[openstack-ansible] os_congress role retirement

Hi everyone. Since congress service has been retired with [1], there's no reason for us to carry on and maintain os_congress role [2] for the inactive project. In case congress service will be revived, we can revert role retirement and continue its support in the future. [1] https://review.opendev.org/#/c/721733/ [2] https://opendev.org/openstack/openstack-ansible-os_congress -- Kind regards, Dmitriy Rabotyagov