enhancement: support route label propagation for Gateway API resources

Summary

Please triage whether the controller should support propagating user-defined route labels when using Gateway API resources.

Current behavior

The current controller appears to preserve object labels for ApisixRoute, but I did not find equivalent propagation for Gateway API route resources such as HTTPRoute.

This means route label based usage patterns available through the APISIX CRD path may not carry over to the Gateway API path.

Use cases affected

• using route labels to drive global-plugin logic or other label-based management workflows
• keeping Gateway API route metadata aligned with the label propagation behavior available on the APISIX CRD side

Code context

• internal/adc/translator/apisixroute.go
• internal/adc/translator/httproute.go