Support Kubernetes Gateway API

[JordanSussman]

Is your feature request related to a problem? Please describe.

Skipper exclusively supports the Kubernetes Ingress API, creating hurdles for users who wish to transition between other providers and Skipper. As the Kubernetes community increasingly migrates Ingress functionality to the Kubernetes Gateway API, aiming to establish a universal standard for Ingress across different providers, it becomes valuable for Skipper to align with this evolution for improved compatibility.

From the Kubernetes Gateway API docs:

Gateway API is an official Kubernetes project focused on L4 and L7 routing in Kubernetes. This project represents the next generation of Kubernetes Ingress, Load Balancing, and Service Mesh APIs. From the outset, it has been designed to be generic, expressive, and role-oriented.

Describe the solution you would like

I'd like Skipper to support the Kubernetes Ingress API and the Kubernetes Gateway API.

Describe alternatives you've considered (optional)

Continue utilizing the Kubernetes Ingress API.

Additional context (optional)

Adding support for the Kubernetes Gateway API would enhance Skipper's flexibility and interoperability with a wider range of Kubernetes networking configurations, providing users with more options for managing ingress traffic.

Would you like to work on it?

I probably won't have the bandwidth to work on most of the modifications, but I'm open to contributing segments of the code if there's someone available to offer guidance.

[szuecs]

Thanks for providing this issue.
I was part of online and offline discussions about gateway api. I think it's complicated and we can't really support all features (tcp routes for example) and our filters will become again annotations to httproute objects. I think it's a step backwards compared to RouteGroup to support this and a lot of work with unclear benefits.

If you want to use more routing features compared to ingress, then you can use RouteGroup as alternative which is much easier and safer than gateway api https://opensource.zalando.com/skipper/kubernetes/routegroup-crd