show actual size (how much it takes up) of the VM OR show "reclaimable space"

because of v3.2.0 (pre-release), trimming the drives in the VM will result in reduced disk usage.
however, that is not reflected in UTM, as the current size UTM shows is the size of the images (disk images) with the holes (i.e. UTM shows apparent size, not actual size).

before reclaim: 

after reclaim: 

solutions:
- show the actual size it would take up on disk (maybe along with the apparent size (refer to [`DU(1)` man page](https://linux.die.net/man/1/du)))
- another is to show the amount of space the disk images can be "reduced" by (it doesn't *actually* get reduced in the sense of disk usage, since the disk image contains holes)