Update tutorial-multiple-sites-cli.md

Command to create application gateway requires priority to be set , else command fails with below error:
```
root@jumpbox:~# az network application-gateway create \
>   --name myAppGateway \
>   --location eastus \
>   --resource-group myResourceGroupAG \
>   --vnet-name myVNet \
>   --subnet myAGsubnet \
>   --capacity 2 \
>   --sku Standard_v2 \
>   --http-settings-cookie-based-affinity Disabled \
>   --frontend-port 80 \
>   --http-settings-port 80 \
>   --http-settings-protocol Http \
>   --public-ip-address myAGPublicIPAddress
{"error":{"code":"InvalidTemplateDeployment","message":"The template deployment 'ag_deploy_3IcTICTZ0Kxfpo4jkw7Qj4g1eWhAlEaV' is not valid according to the validation procedure. The tracking id is '4ebf7211-543f-4ed7-83b3-76cbb55d32d3'. See inner errors for details.","details":[{"code":"ApplicationGatewayRequestRoutingRulePriorityCannotBeEmpty","message":"Priority for the request routing rule /subscriptions/4ff5187b-445f-4080-a09f-5565e458d856/resourceGroups/myResourceGroupAG/providers/Microsoft.Network/applicationGateways/myAppGateway/requestRoutingRules/rule1 cannot be empty. All request routing rules should have a priority defined starting from api-version 2021-08-01","details":[]}]}}
```
added --priority 10 option to command to produce successful result

Author: raghushukla1

articles/application-gateway/tutorial-multiple-sites-cli.md

@@ -88,7 +88,8 @@ az network application-gateway create \
   --frontend-port 80 \
   --http-settings-port 80 \
   --http-settings-protocol Http \
-  --public-ip-address myAGPublicIPAddress
+  --public-ip-address myAGPublicIPAddress \
+  --priority 10
 ```
 
 It may take several minutes for the application gateway to be created. After the application gateway is created, you can see these new features of it: