--Destination-addresses with servicetag in lowercase gets listed under IP Addresses instead of Service Tags

- If the issue is to do with Azure CLI 2.0 in-particular, create an issue here at [Azure/azure-cli](https://github.com/Azure/azure-cli/issues)

### Extension name (the extension in question)
az network firewall network-rule

### Description of issue (in as much detail as possible)
if --destination-addresses includes a service tag in lower case (AzureCloud.**b**razil**s**outh) the rule ends up under IP addresses instead of Service tags in the Network rule collection.

I'm able to reproduce the issue using Cloudshell and CLI. Here’s the commands/results

This rule goes under 'IP addresses' in the network rule collection:
az network firewall network-rule create -g azfw --collection-name NetworkRule --source-addresses 10.5.5.5 --destination-ports 10225 --firewall-name azfw --name test --protocols UDP --destination-addresses AzureCloud.**b**razil**s**outh

This rule goes under Service Tags in the network rule collection
az network firewall network-rule create -g azfw --collection-name NetworkRule --source-addresses 10.5.5.5 --destination-ports 10225 --firewall-name azfw --name test2 --protocols UDP --destination-addresses AzureCloud. **B**razil**S**outh

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