[BUG] Support Kubernetes Gateway API

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Current Behavior

ShenYu currently supports Kubernetes Ingress resource for service discovery and routing. However, Ingress is no longer recommended, the Gateway API is the next-generation Kubernetes networking standard, providing more expressive and role-oriented routing capabilities (GatewayClass, Gateway, HTTPRoute, etc.).

### Expected Behavior

_No response_

### Steps To Reproduce

_No response_

### Environment

```markdown
ShenYu version(s):
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### Debug logs

_No response_

### Anything else?

_No response_

Start by reviewing ShenYu's existing Kubernetes Ingress support and how it performs service discovery and routing. Then study the Gateway API resources named in the issue—GatewayClass, Gateway, and HTTPRoute—and define support for them while preserving the existing routing behavior; no specific files or tests are named.

Written by the indexing model from the issue text.