e2e: add retry/failover test configuration files

Add 13 test-specific plano configs covering:
- Basic 429/503 retry scenarios
- Multi-provider failover with priority ordering
- Max attempts and backoff delay verification
- Retry-After header honoring and blocking
- Timeout-triggered retry
- High latency failover
- Streaming retry
- Request body preservation across retries

Signed-off-by: Troy Mitchell <i@troy-y.org>

tests/e2e/configs/retry_it7_fallback_priority.yaml

@@ -0,0 +1,28 @@
+version: v0.3.0
+
+listeners:
+  - type: model
+    name: model_listener
+    port: 12000
+
+model_providers:
+  - model: openai/gpt-4o
+    base_url: http://host.docker.internal:${MOCK_PRIMARY_PORT}
+    access_key: test-key-primary
+    default: true
+    retry_policy:
+      fallback_models: [anthropic/claude-3-5-sonnet, mistral/mistral-large]
+      default_strategy: "different_provider"
+      default_max_attempts: 3
+      on_status_codes:
+        - codes: [429]
+          strategy: "different_provider"
+          max_attempts: 3
+
+  - model: anthropic/claude-3-5-sonnet
+    base_url: http://host.docker.internal:${MOCK_FALLBACK1_PORT}
+    access_key: test-key-fallback1
+
+  - model: mistral/mistral-large
+    base_url: http://host.docker.internal:${MOCK_FALLBACK2_PORT}
+    access_key: test-key-fallback2