[Feature]: update the subnet properties directly without using "Get-AzVirtualNetwork/Set-AzVirtualNetwork"

### Description of the new feature

when we delete the subnet via the PowerShell command, we have to execute the “Get/Set- AzVirtualNetwork ” command. it will trigger the put operation to the ARM on the “VIRTUALNETWORKS” level.

$vnet=Get-AzVirtualNetwork -Name XXX -ResourceGroupName XXX
Remove-AzVirtualNetworkSubnetConfig -Name XXX -VirtualNetwork $vnet
$vnet| Set-AzVirtualNetwork

Operation name: PUT/SUBSCRIPTIONS/RESOURCEGROUPS/PROVIDERS/MICROSOFT.NETWORK/VIRTUALNETWORKS/

Additional permission is required for the VNET operation if the DDOS plan is enabled. e.g “Microsoft.Network/ddosProtectionPlans/join/action permission"

can we have the feature to perform the “VIRTUALNETWORKS/SUBNETS” level operation directly via PowerShell?
when we change the subnet configuration from the portal or CLI, only the subnet properties will be sent to the ARM.
operation name will be "PUT/SUBSCRIPTIONS/RESOURCEGROUPS/PROVIDERS/MICROSOFT.NETWORK**/VIRTUALNETWORKS/SUBNETS/"

### Proposed implementation details (optional)

when we change the subnet configuration from the portal or CLI, only the subnet properties will be sent to the ARM.
operation name will be "PUT/SUBSCRIPTIONS/RESOURCEGROUPS/PROVIDERS/MICROSOFT.NETWORK**/VIRTUALNETWORKS/SUBNETS/"