switch from grub to systemd bootloader

[LnxBil]

I can recommend to create your hetzner system inside of your local PVE setup with UEFI disks and copy it up. I did this sucessfully multiple times.

local system:
- create a VM with small two 16 GB disks and use EFI as the machine type
- install PVE in mirrored ZFS mode
- power off your VM

hetzner system:
- boot into rescue mode
- copy your local system disks via ssh dd directly onto your disks
- fix GPT
- reboot

Hopefully, your system will just boot. Afterwards resize your ZFS partion to the maximum and expand your ZFS to the whole disk.