feat(aula-14): adicionar Istio Traffic Splitting com canary deployment

- Instala Istio (base + istiod + ingressgateway)
- Configura Kiali e Jaeger para observabilidade
- Deploy de app-backend v1 e v2 com traffic splitting 90/10
- Integra com Victoria Metrics da aula-12
- Inclui teste-stress.sh para validar distribuição de tráfego
- Tráfego externo passa pelo Istio Gateway via NGINX Ingress

aula-14/istio/gateway.yaml

@@ -0,0 +1,36 @@
+apiVersion: networking.istio.io/v1beta1
+kind: Gateway
+metadata:
+  name: app-backend-gateway
+  namespace: istio
+spec:
+  selector:
+    istio: ingressgateway
+  servers:
+    - port:
+        number: 80
+        name: http
+        protocol: HTTP
+      hosts:
+        - "${APP_HOST}"
+---
+apiVersion: networking.istio.io/v1beta1
+kind: VirtualService
+metadata:
+  name: app-backend-external
+  namespace: istio
+spec:
+  hosts:
+    - "${APP_HOST}"
+  gateways:
+    - app-backend-gateway
+  http:
+    - route:
+        - destination:
+            host: app-backend
+            subset: v1
+          weight: 90
+        - destination:
+            host: app-backend
+            subset: v2
+          weight: 10