fix(aibrix): add default_decision to aibrix values.yaml for PII fallback

The aibrix profile uses static YAML configuration (not CRDs). The PII policy
checker has a fallback to 'default_decision' when no decision name is provided,
but aibrix didn't define this decision. This caused all PII detection requests
to be allowed (0% accuracy).

Adding default_decision with PII enabled (pii_types_allowed: []) ensures that
the fallback logic works correctly for aibrix, matching the behavior expected
by the E2E PII detection tests.

Related to #648

Signed-off-by: Yossi Ovadia <[email protected]>

Author: yossiovadia

deploy/kubernetes/aibrix/semantic-router-values/values.yaml

@@ -380,6 +380,23 @@ config:
             system_prompt: "You are a thinking expert, should think multiple steps before answering. Please answer the question step by step."
             mode: "replace"
 
+    - name: default_decision
+      description: "Default fallback decision for requests without specific routing"
+      priority: 1
+      rules:
+        operator: "OR"
+        conditions:
+          - type: "domain"
+            name: "other"
+      modelRefs:
+        - model: vllm-llama3-8b-instruct
+          use_reasoning: false
+      plugins:
+        - type: "pii"
+          configuration:
+            enabled: true
+            pii_types_allowed: []
+
   # Strategy for selecting between multiple matching decisions
   # Options: "priority" (use decision with highest priority) or "confidence" (use decision with highest confidence)
   strategy: "priority"