Add Unhealthy CustomDomainStatus for StaticSites (#18557)

Author: joslinmicrosoft

specification/web/resource-manager/Microsoft.Web/stable/2022-03-01/StaticSites.json

@@ -3120,7 +3120,8 @@
                 "Adding",
                 "Ready",
                 "Failed",
-                "Deleting"
+                "Deleting",
+                "Unhealthy"
               ],
               "type": "string",
               "readOnly": true,