Update Gateway API docs

[buraksekili]

Background

In KKP 2.31, Gateway API (with Envoy Gateway) will become the only supported way to route external traffic to the Kubermatic dashboard, API, and related services. The nginx-ingress-controller option is being a no-op in the source code entirely.

1. Auto-generated KubermaticConfiguration Reference Files: like data/kubermaticConfiguration.yaml needs updates, and we need to remove the ingress configuration block (lines ~238-261 in each file) which contains:

• className: nginx
• disable: false
• certificateIssuer configuration tied to Ingress
• namespaceOverride

Note that since those configuration files are auto-generated, do not manually edit them

2. Installation Guide: The configurations in installation guide should be updated for 2.31. Update them to match the new Gateway API configuration paths.
3. Setup Checklist: Update checklist to respect the new Gateway API
4. Custom Certificates Guide
5. Architecture Networking Concept Page: This page primarily covers expose strategies (NodePort, LoadBalancer, Tunneling) which are not affected by the nginx removal. Review and consider adding a brief mention that KKP uses Gateway API (Envoy Gateway) for management cluster ingress, replacing any implied nginx assumption.

[buraksekili]

/milestone KKP 2.31

[kubermatic-bot]

@buraksekili: The provided milestone is not valid for this repository. Milestones in this repository: [KKP 2.21, KKP 2.29, KKP 2.30, KubeOne 1.5]

Use /milestone clear to clear the milestone.

Details

In response to this:

/milestone KKP 2.31

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