Enable HyperVGeneration version 2 for Azure disks

User Story:

As a user, I want to be able to:

• Create VM on Azure with HyperVGeneration version 2

so that I can

• Use extra features on the VM disks like larger disk size, secure booting etc.

Acceptance Criteria:

Description of criteria:

• Should be able to create a cluster with disk HyperVGeneration V2 using a gen 2 image and a VM instance type that supports gen 2.
• Validation of the VM instance type to check if it supports V2 is needed.
• Compute nodes are able to be created with gen2
• Both Gen1 and Gen2 instances can be created in the cluster
• Doc update for how to specify correct image in a scaleup (a card to update this is fine)

Engineering Details:

• Currently we are using V1 by default. A variable must be set and used in Terraform here. https://github.com/openshift/installer/blob/master/data/data/azure/vnet/main.tf#L94-L104