[kuryr] Deprecation of Ingress support and namespace isolation

Hi, I've decided to put up a patch [1] deprecating the aforementioned features. It's motivated by the fact that there are better ways to do both: * Ingress can be done by another controller or through cloud provider. * Namespace isolation can be achieved through network policies. Both alternative ways are way better tested and there's nobody maintaining the deprecated features. I'm open to keep them if someone using them steps up. With the fact that Kuryr seems to be tied more with Kubernetes releases than with OpenStack ones and given there will be no objections, we might start removing the code in the Ussuri timeframe. [1] https://review.opendev.org/#/c/703420/ Thanks, Michał