[TUTORIAL] HOWTO: Proxmox host serial console (UEFI-boot), useful when passthrough your only GPU

Hey there, everyone.

I'm installing a new VM tonight with Ubuntu 24.04 LTS. I wanted to enable a virtual serial port inside the VM, so I set one up in Proxmox.

I added the `console=tty0 console=ttyS#,115200n8` to the GRUB config and updated GRUB and the initramfs, and rebooted.
It automatically created the systemd service we had to manually create in the OP, and i was off to the races with a serial console that I could watch the VM boot up on.

This seems like a lot slicker approach than manually creating systemd units. I vaguely recall it was always supposed to be automatic like this, but just wasn't in earlier versions of Proxmox and some Linux VMs.