This is meant to be used in the Hetzner cloud sandbox project, so SSH
keys can be injected when a new VM is created from e.g. a CI pipeline,
so that the CI pipeline can SSH to the newly created VM.

The EC2 metadata service is used over the Hetzner metadata service, as
it is supported by more providers (including Hetzner).

As of version 1.7.0, HCL2 is the preferred way to write Packer
templates. The documentation reflect this and it is easier if we use the
preferred format.

- 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