feat(validator): add Kubeflow Trainer to robust-controller and skip inference-gateway on training clusters

[yuanchen8911]

Summary

• Add Kubeflow Trainer as an alternative target for the robust-controller CNCF conformance check
• Skip inference-gateway check on training clusters (no kgateway)
• Add Kubeflow Trainer support to evidence collection script (collect-evidence.sh)
• Skip inference gateway evidence collection when kgateway is not installed

Problem

1. robust-controller: Only validated Dynamo operator, skipping on all training clusters (EKS and GKE)
2. inference-gateway: Failed with "GatewayClass 'kgateway' not found" on training clusters instead of skipping gracefully

Changes

robust-controller (Go + evidence script)

Check selects target based on recipe component presence:

• dynamo-platform in recipe → validate Dynamo operator (existing)
• kubeflow-trainer in recipe → validate Kubeflow Trainer (new)
• neither → skip

Kubeflow Trainer validation:

1. Controller deployment running (kubeflow-trainer-controller-manager)
2. Validating webhook operational — exact match on validator.trainer.kubeflow.org
3. TrainJob CRD exists (trainjobs.trainer.kubeflow.org)
4. Webhook rejects invalid TrainJob (non-existent runtimeRef, proves webhook logic)

Evidence script (collect-evidence.sh):

• Auto-detects Dynamo vs Kubeflow Trainer
• Collects deployment health, CRDs, webhook verification, rejection test

inference-gateway (Go + evidence script)

• Skip when kgateway component is not in recipe (training clusters)
• Evidence script skips when kgateway deployment not found

Test plan

• Unit tests: TestRecipeHasComponent (5 cases), TestCheckRobustControllerRouting (6 cases)
• go build, go vet, gofmt clean
• E2E: GKE training cluster — robust-controller PASSED (Kubeflow Trainer)
• E2E: EKS training cluster — robust-controller PASSED (Kubeflow Trainer)
• E2E: EKS inference cluster — robust-controller PASSED (Dynamo)
• Evidence collection: robust-operator.md generated with Kubeflow Trainer evidence
• No regressions on Dynamo path