Build the OpenVPN AMI on a Graviton (AMD64) instance

[jsf9k]

🗣 Description

This pull request modifies the Packer code to build the OpenVPN AMI on a Graviton (AMD64) instance.

💭 Motivation and context

Running the AMI on Graviton should be cheaper and better for the environment.

🧪 Testing

All automated tests pass. I also built a staging AMI with these changes and verified that it functions as expected.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• All new and existing tests pass.
• Build and test a staging AMI with these changes.

✅ Pre-merge checklist

• Finalize version.

✅ Post-merge checklist

• Create a release.

[jsf9k]

The CDM Nessus agent does not support ARM64 on Debian, although it does on Ubuntu.

[mcdonnnj]

The CDM Nessus agent does not support ARM64 on Debian, although it does on Ubuntu.

Do you think the Ubuntu package may work given the relationship between Ubuntu and Debian?

[jsf9k]

The CDM Nessus agent does not support ARM64 on Debian, although it does on Ubuntu.

Do you think the Ubuntu package may work given the relationship between Ubuntu and Debian?

My thought was to convert to an Ubuntu base AMI instead of restoring to such chicanery.

[jsf9k]

Closed in favor of #112.