feat(conformance): Add HTTPRoute port validation tests for InferencePool backends

[zetxqx]

Adds new conformance tests (InferencePoolHTTPRoutePortValidation) to verify HTTPRoute.spec.rules.backendRefs.port behavior with InferencePool backends. Covers scenarios for unspecified, matching, and non-matching ports.

This PR is originally from #887 to address #886. Based on the discussion #918 , now the test is updated to

1. HTTPRoute.BackendRef.Port unspecified, gateway can send traffic successfully.
2. HTTPRoute.BackendRef.Port is set and equals to InferencePool.TargetPortNumber, gateway can send traffic successfully.
3. HTTPRoute.BackendRef.Port is set and not equal to InferencePool.TargetPortNumber, gateway can still send traffic successfully.

One missing part is for case3, we need to verify there is warning in httpRoute mentioned in Option5 from #918

Testing against istio:

go test -v ./conformance -args -debug -gateway-class istio -cleanup-base-resources=false -run-test InferencePoolHTTPRoutePortValidation

=== RUN   TestConformance
...
--- PASS: TestConformance (16.07s)
    --- SKIP: TestConformance/HTTPRouteInvalidInferencePoolRef (0.00s)
    --- SKIP: TestConformance/InferencePoolAccepted (0.00s)
    --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation (13.05s)
        --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation/Scenario_1:_HTTPRoute_backendRef_to_InferencePool_with_Port_Unspecified (10.41s)
        --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation/Scenario_2:_HTTPRoute_backendRef_to_InferencePool_with_Port_Specified_and_Matching (0.10s)
        --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation/Scenario_3:_HTTPRoute_backendRef_to_InferencePool_with_Port_Specified_and_Non-Matching._Request_still_passing_because_HTTP_Port_is_ignored_when_inferencePool_is_backendRef (0.34s)
    --- SKIP: TestConformance/InferencePoolResolvedRefsCondition (0.00s)

Testing against gke-l7-regional-external-managed

go test -v ./conformance -args -debug -gateway-class gke-l7-regional-external-managed -cleanup-base-resources=false -run-test InferencePoolHTTPRoutePortValidation

=== RUN   TestConformance/InferencePoolResolvedRefsCondition
    conformance.go:68: Skipping InferencePoolResolvedRefsCondition: test explicitly skipped
--- PASS: TestConformance (280.47s)
    --- SKIP: TestConformance/HTTPRouteInvalidInferencePoolRef (0.00s)
    --- SKIP: TestConformance/InferencePoolAccepted (0.00s)
    --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation (276.86s)
        --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation/Scenario_1:_HTTPRoute_backendRef_to_InferencePool_with_Port_Unspecified (274.23s)
        --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation/Scenario_2:_HTTPRoute_backendRef_to_InferencePool_with_Port_Specified_and_Matching (0.11s)
        --- PASS: TestConformance/InferencePoolHTTPRoutePortValidation/Scenario_3:_HTTPRoute_backendRef_to_InferencePool_with_Port_Specified_and_Non-Matching._Request_still_passing_because_HTTP_Port_is_ignored_when_inferencePool_is_backendRef (0.10s)
    --- SKIP: TestConformance/InferencePoolResolvedRefsCondition (0.00s)

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[ahg-g]

/ok-to-test

[zetxqx]

@robscott This is also ready for review. Thanks in advance!

[zetxqx]

These will be refactored to a common place. But for this PR itself, I would like to keep it as is for making the focus of this PR clear.

[nirrozenbaum]

/test pull-gateway-api-inference-extension-test-e2e-main

[danehans]

One missing part is for case3, we need to verify there is warning in httpRoute mentioned in Option5 from #918

This warning message will need to be defined in Gateway API, so the standard message can be asserted in conformance tests. @robscott should we proceed with option 3 from the discussion until the message is standardized in v1.4 of Gateway API?

[robscott]

This warning message will need to be defined in Gateway API, so the standard message can be asserted in conformance tests. @robscott should we proceed with option 3 from the discussion until the message is standardized in v1.4 of Gateway API?

IMO, "Gateway implementations put a warning on HTTPRoute status when HTTPRoute.BackendRef.Port is set and an InferencePool is targeted, saying that the port will be ignored" from option 5 is something that works now and in the future. After Gateway v1.4 is released, we won't be able to test this because Gateway API CRDs will prevent this from being possible, so maybe we should leave it out of conformance tests altogether.

[zetxqx]

@robscott I agree with "we should leave it out of conformance tests altogether". The current PR doesn't have that check. So is it good to get a LG?