Update packer build and use smaller BIOS boot partition

• Create packer builder in FSN1 and change image to ubuntu-20.04
• Add "use_proxy: false" to provisioner config to work around [1]
• Reduce the size of the BIOS boot partition to 1M (from 10M) [2]
• Update bootstrap_version to 2022.03.01

[1] https://github.com/hashicorp/packer-plugin-ansible/issues/69
[2] https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html