feat(vm): hotplug cpu (phase 1)

[diafour]

Description

• Change cpu cores setting from domain.resources/limits to domain.cpu fields.
• Support old VMs to not require reboot on module update.

This PR is a support of new "dynamic cores strategy" implemented in PR deckhouse/3p-kubevirt#82

Why do we need it, and what problem does it solve?

It is a phase 1 of implementation of the CPU hotplug support.

Limitations:

• No additional VMClass settings, only spec.cpu.cores in the VM is supported for now.
• Should be explicitly enabled via specifying a featureGate in the ModuleConfig.

Main difference from original Kubevirt:

• Dynamic cores, static sockets count: 1-16 cores 1 socket, 18-32 cores 2 sockets, etc.
• CPU cores reducing is allowed.
• Main Pod and target Pod always have resources.limits for CPU.

What is the expected result?

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vm
type: feature
summary: "Simple implementation of CPU hotplug"

[LopatinDmitr]

• Replace
  if featuregates.Default().Enabled(featuregates.HotplugMemoryWithLiveMigration) {
  on

    if featuregates.Default().Enabled(featuregates.HotplugMemoryWithLiveMigration) || 
     featuregates.Default().Enabled(featuregates.HotplugCPUWithLiveMigration) {                          
  ``
  

• in sync_kvvm.go is still a Patch → Update
• kvbuilder.SetCPU() uses a global feature gate, comparator uses an injectable one
• Support for “old VMs" is tied only to PrintableStatus == Running.