[Doc]: New-AzContainerInstanceVolumeMountObject should be called before creating a ACI container group with New-AzContainerGroup to mount Azure File share

### Description

https://docs.microsoft.com/en-us/powershell/module/az.containerinstance/new-azcontainergroup?view=azps-7.1.0#example-6--create-a-container-group-that-mounts-azure-file-volume

Cmdlet reference for New-AzContainerGroup shows how to create a container group that mounts Azure Files with below sequence.
```
$volume = New-AzContainerGroupVolumeObject -Name "myvolume" -AzureFileShareName "myshare" -AzureFileStorageAccountName "username" -AzureFileStorageAccountKey (ConvertTo-SecureString "PlainTextPassword" -AsPlainText -Force)
$container = New-AzContainerInstanceObject -Name test-container -Image alpine
$containerGroup = New-AzContainerGroup -ResourceGroupName test-rg -Name test-cg -Location eastus -Container
$container -Volume $volume
```

However this sequence does not let a container mount Azure File volume.
New-AzContainerInstanceVolumeMountObject should be used in advance like below;

```
$volume = New-AzContainerGroupVolumeObject -Name "myvolume" -AzureFileShareName "myshare" -AzureFileStorageAccountName "username" -AzureFileStorageAccountKey (ConvertTo-SecureString "PlainTextPassword" -AsPlainText -Force)
$mount = New-AzContainerInstanceVolumeMountObject -MountPath "/aci/logs" -Name "myvolume"
$container = New-AzContainerInstanceObject -Name test-container -Image alpine -VolumeMount $mount
$containerGroup = New-AzContainerGroup -ResourceGroupName test-rg -Name test-cg -Location eastus -Container $container -Volume $volume
```