Expose NodeSelector for VirtualMachines with kubevirt provider

Currently there is no option to influence on the placement of the VMs of an hosted cluster with kubevirt provider. the existing NodeSelector in HostedCluster are influencing only the pods in the hosted control plane namespace.

The goal is to introduce an new field in .spec.platform.kubevirt stanza in NodePool for node selector, propagate it to the VirtualMachineSpecTemplate, and expose this in the hypershift and hcp CLIs.