add routing service (#814)

fixes https://github.com/katanemo/plano/issues/810

demos/llm_routing/model_routing_service/config.yaml

@@ -0,0 +1,27 @@
+version: v0.3.0
+
+listeners:
+  - type: model
+    name: model_listener
+    port: 12000
+
+model_providers:
+
+  - model: openai/gpt-4o-mini
+    access_key: $OPENAI_API_KEY
+    default: true
+
+  - model: openai/gpt-4o
+    access_key: $OPENAI_API_KEY
+    routing_preferences:
+      - name: complex_reasoning
+        description: complex reasoning tasks, multi-step analysis, or detailed explanations
+
+  - model: anthropic/claude-sonnet-4-20250514
+    access_key: $ANTHROPIC_API_KEY
+    routing_preferences:
+      - name: code_generation
+        description: generating new code, writing functions, or creating boilerplate
+
+tracing:
+  random_sampling: 100