refactor: split qemu_machine_feature_enabled

refactor: split qemu_machine_feature_enabled

...into:

* PVE::QemuServer::Helpers::min_version: check a major.minor version
  string with a given major/minor version (this is equivalent to calling
  the old qemu_machine_feature_enabled with only $kvmver)
* PVE::QemuServer::Machine::extract_version: get major.minor version
  string from arbitrary machine type (e.g. pc-q35-4.0, ...)
* PVE::QemuServer::Machine::machine_version: helper to call
  extract_version automatically before min_version

Includes a cfg2cmd test case with pinned machine version.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>