So I figured out how to use Packer with QEMU to create customized Ubuntu Live Server Images along with Bootloader sequencing. I have documented it and also created a repository for someone to take future inspiration.
Blog: Customized Ubuntu Images using Packer + QEMU + Cloud-Init & UEFI bootloading - Shan's Corner
GitHub Repo: GitHub - shantanoo-desai/packer-ubuntu-server-uefi: Templates for creating Ubuntu Live Server Images (20.04.4 / 22.04.2) with Packer + QEMU + Autoinstall (cloud-init)