Migrate prow from ingress-nginx

[lentzi90]

Ingress-nginx is being retired: https://www.kubernetes.dev/blog/2025/11/12/ingress-nginx-retirement/
We should switch to something else before Marsh 2026.
I think the best option is to migrate to Gateway API. However, we could also switch to another Ingress controller (e.g. haproxy). That would be much less work, but considering that Gateway API is supposed to be the successor of Ingress in the long term, it probably makes more sense to migrate to that anyway.

There are plenty of implementations of the Gateway API. See the list at https://gateway-api.sigs.k8s.io/implementations/#gateway-controller-implementation-status.

[tuminoid]

+1 for Gateway API, no point in rewriting anything to Ingress anymore. There are even tools in Gateway API project to migrate Ingress files so it should be quite clean transition.

[tuminoid]

/triage accepted