Unauthorized route migration for routes owned by appex-ai-infra (#214777)

### Authz API migration for unauthorized routes

This PR migrates last unauthorized routes owned by your team to a new
security configuration.
Please refer to the documentation for more information: [Authorization
API](https://docs.elastic.dev/kibana-dev-docs/key-concepts/security-api-authorization)

### **Before migration:**
```ts
router.get({
  path: '/api/path',
  ...
}, handler);
```

### **After migration:**
```ts
router.get({
  path: '/api/path',
  security: {
    authz: {
      enabled: false,
      reason: 'This route is opted out from authorization because ...',
    },
  },
  ...
}, handler);
```

x-pack/platform/plugins/shared/inference/server/routes/chat_complete.ts

@@ -166,6 +166,12 @@ export function registerChatCompleteRoute({
   router.post(
     {
       path: '/internal/inference/chat_complete/stream',
+      security: {
+        authz: {
+          enabled: false,
+          reason: 'This route delegates authorization to the inference client',
+        },
+      },
       validate: {
         body: chatCompleteBodySchema,
       },