Change load balancer image in smoke test (#3740)

test/e2e/static_resources/loadbalancer.yaml

@@ -15,7 +15,8 @@ spec:
     spec:
       containers:
         - name: nginx
-          image: nginx
+          image: mcr.microsoft.com/cbl-mariner/base/nginx:1
+          command: ["/bin/sh", "-c", "mkdir -p /usr/share/nginx/html && echo 'hello world' > /usr/share/nginx/html/index.html && nginx -g 'daemon off;'"]
           ports:
             - containerPort: 80
               name: http-web-svc