Allow building other than Legacy-BIOS-only Proxmox images.
Default is unchanged.
To build UEFI proxmox image use:
proxmox.qemuConf.bios = "ovmf";
(default is "seabios")
To build image bootable using both "seabios" and "ovmf" use:
partitionTableType = "hybrid";
BIOS can be switched in Proxmox between "seabios" and "ovmf" and VM still boots.
(GRUB2-only, systemd-boot does not boot under "seabios")
To build systemd-boot UEFI image:
proxmox.qemuConf.bios = "ovmf";
boot.loader.systemd-boot.enable = true;
