file-restore: dynamically increase memory of vm for zpools

file-restore: dynamically increase memory of vm for zpools

when a backup contains a drive with zfs on it, the default memory
size (up to 384 MiB) is often not enough to hold the zfs metadata

to improve that situation, add memory dynamically (1GiB) when a path is
requested that is on zfs. Note that the image must be started with a
kernel capable of memory hotplug.

to achieve that, we also have to add a qmp socket to the vm, so that
we can later connect and add the memory backend and dimm

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>