Support memory ballooning in VMs

### Description

I have a VM which uses approximately half of its allocated memory most of the time but sometimes spikes up near the allocated memory limit. To ensure uninterrupted execution of processes inside the VM, I have to allocate much more memory than the VM needs most of the time.

This could be improved if Lima VMs released unused memory automatically without user intervention.

Lima doesn't support memory ballooning currently. Apple docs [indicate](https://developer.apple.com/documentation/virtualization/vzvirtualmachineconfiguration/memoryballoondevices) that VZ supports this but I'm not sure of the scope of the changes required.

Relevant discussion: https://github.com/lima-vm/lima/discussions/2720