VM support for IP forwarding and accelerated networking.

[ninjarobot]

The changes in this PR are as follows:

• Virtual Machines: Accelerated networking and IP forwarding for interfaces

I have read the contributing guidelines and have completed the following:

• [x] Tested my code end-to-end against a live Azure subscription.
• [x] Updated the documentation in the docs folder for the affected changes.
• [x] Written unit tests against the modified code that I have made.
• [x] Updated the release notes with a new entry for this PR.
• [x] Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

arm {
    location Location.EastUS
    add_resources
        [
            vm {
                name "network-appliance"
                username "azureuser"
                operating_system UbuntuServer_2004LTS
                vm_size Standard_D2s_v5
                spot_instance Deallocate

                // Enabling accelerated networking requires a D-series or similar with multiple vCPUs
                accelerated_networking Enabled
                ip_forwarding Enabled
            }
        ]
}