Add guide for the breaking change of resource google_compute_autoscaler (#8648) (#6085)

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/8648.txt

@@ -0,0 +1,3 @@
+```release-note:none
+
+```

website/docs/guides/version_5_upgrade.html.markdown

@@ -205,3 +205,8 @@ it will use the default value from the API which is `FALSE`. If you want to
 enable endpoint independent mapping, then explicity set the value of
 `enable_endpoint_independent_mapping` field to `TRUE`.
 
+## Resource: `google_compute_autoscaler` (beta)
+
+### `metric.filter` now defaults to `resource.type = gce_instance`
+
+Previously, `metric.filter` doesn't have the defult value and causes a UI error.