enhancement: support attaching L4 plugins with Gateway API routes

[kayx23]

Summary

Please triage whether the controller should support attaching L4 plugins when using Gateway API L4 routes.

Current behavior

APISIX itself supports attaching stream plugins to stream_routes, for example limit-conn, ip-restriction, mqtt-proxy, syslog, and traffic-split.

However, the current Gateway API surface in the controller does not expose an equivalent way to attach plugins for L4 routes.

In the current translator paths:

• HTTPRoute and GRPCRoute have plugin/filter handling paths
• TCPRoute, UDPRoute, and TLSRoute build upstreams and attach BackendTrafficPolicy
• there is no comparable plugin attachment mechanism for Gateway API L4 routes

As a result, L4 plugin scenarios supported by APISIX cannot currently be expressed through Gateway API resources in the controller.

Use cases affected

• attaching stream plugins to Gateway API L4 routes
• managing L4 routing and L4 plugin behavior through the same Gateway API-oriented configuration flow

Code context

• APISIX stream plugin list: apisix/cli/config.lua
• internal/adc/translator/tcproute.go
• internal/adc/translator/udproute.go
• internal/adc/translator/tlsroute.go

[coderabbitai]

🔗 Related PRs

#387 - feat: support skip gatewayapi v1alpha2 [merged]

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