Use Standard IP SKU by default for edge case with private_virtual_network_with_public_ip field

[JenGoldstrich]

This PR fixes an issue raised where the private_virtual_network_with_public_ip field that allows users to bring their own vnet, and have the plugin create a public IP, subnet.

This is a breaking change, as the default behavior for this for this field will change, but on March 31st 2025 https://azure.microsoft.com/en-us/updates?id=upgrade-to-standard-sku-public-ip-addresses-in-azure-by-30-september-2025-basic-sku-will-be-retired Azure is removing the ability to create these IPs, so we don't have much of a choice but to make a breaking change, users can roll back by setting the public_ip_sku field to basic, if they want to use the newest plugin version, but still create basic IP skus.

Following up we should address this issue #468, which basically requests having the plugin creates the Network Security Group (NSG). But I didn't wanna delay rolling out this fix in the mean time.

The requestor had a good suggestion in the other linked issue to assign it at the NIC level, doing some reading I've learned that this can have some unexpected side effects as the NIC NSG can conflict with the Subnet NSG. The default behavior should be to encourage users to create their own NSGs in this situation, since they're managing their own vnet, but we should add support for creating an NSG at the NIC level, for users who do not want to create this security group (or those that do not know their build machine's IP ahead of time, and want to explicitly only allow that build VM)

Closes #458

[JenGoldstrich]

We no longer need to check the vnet or private IP status here, because we simply moved the public IP sku block up above the check that removes the public IP. So if the public IP shouldn't be here we remove it when we call builder.SetVirtualNetwork