update external link (Azure#15273)

Author: xiangyan99

sdk/metricsadvisor/azure-ai-metricsadvisor/README.md

@@ -454,7 +454,7 @@ hook = client.create_hook(
         name="email hook",
         description="my email hook",
         emails_to_alert=["alertme@alertme.com"],
-        external_link="https://adwiki.azurewebsites.net/articles/howto/alerts/create-hooks.html"
+        external_link="https://docs.microsoft.com/en-us/azure/cognitive-services/metrics-advisor/how-tos/alerts"
     )
 )
 ```

sdk/metricsadvisor/azure-ai-metricsadvisor/samples/async_samples/sample_hooks_async.py

@@ -45,7 +45,7 @@ async def sample_create_hook_async():
                 name="email hook",
                 description="my email hook",
                 emails_to_alert=["alertme@alertme.com"],
-                external_link="https://adwiki.azurewebsites.net/articles/howto/alerts/create-hooks.html"
+                external_link="https://docs.microsoft.com/en-us/azure/cognitive-services/metrics-advisor/how-tos/alerts"
             )
         )
 

sdk/metricsadvisor/azure-ai-metricsadvisor/samples/sample_hooks.py

@@ -42,7 +42,7 @@ def sample_create_hook():
             name="email hook",
             description="my email hook",
             emails_to_alert=["alertme@alertme.com"],
-            external_link="https://adwiki.azurewebsites.net/articles/howto/alerts/create-hooks.html"
+            external_link="https://docs.microsoft.com/en-us/azure/cognitive-services/metrics-advisor/how-tos/alerts"
         )
     )