VMM Events: Streamline logging

The VMM implements various API events: boot, resize_zone, resize_disk, ... we should add streamlined logging to every event, such as

```rust
fn vm_resize_disk(&mut self, id: String, desired_size: u64) -> result::Result<(), VmError> {
        info!("request to resize disk: id={id}");
        ...
        event!("vm", "disk {id} resized")
```