Add alert definition navigation property to alert configuration (Azure#21249)

Author: juliawelborn

specification/authorization/resource-manager/Microsoft.Authorization/preview/2022-08-01-preview/RoleManagementAlerts.json

@@ -929,6 +929,11 @@
           "type": "string",
           "readOnly": false,
           "description": "The alert configuration type."
+        },
+        "alertDefinition": {
+          "$ref": "#/definitions/AlertDefinition",
+          "readOnly": true,
+          "description": "The alert definition."
         }
       },
       "required": [