Document Advanced Routing - AI Conformance

[csengerszabo]

Provide clear documentation and examples of how to use the Gateway API inference extension for model-aware routing and other advanced inference traffic patterns.

Placement:

• in KubeLB docs
• in KKP docs, within a KubeLB section

Related to: https://github.com/kubermatic/kubelb-ee/issues/204