vm-configurator: Add vsock device
The VSOCK socket address family allows communication on Linux between VM and host without any network configuration. This has been supported in QEMU since 2.8 and libvirt since 7.1.0. Enable the interface automatically on new and existing VMs with automatic context identifiers (CIDs). Unfortunately, there's no vsock device in GVirConfig, so this has to be handled in XML.
Fixes #1091