Update import artifacts to use the new github registry namespace

Current Behavior

Import artifacts currently uses docker.pkg.github.com to determine if a download is coming from the Github container registry and use the GITHUB_ROBOT_USER and GITHUB_ROBOT_PASSWORD credentials.

Purpose

Import artifacts should use the updated namespace: https://ghcr.io to determine if an artifact should be downloaded with the Github robot creds. We should also update the code to make docker_download generic so we can use it for github container registry downloads as well.

Plan

• Continue supporting the old github namespace
• Log warning when using deprecated namespace
• Genericize docker_download so it can be used with the Github robot creds
• Update github download to use docker_download
• Update github download to use both namespaces for the github container registry
• Update this document to reflect these updates

Acceptance Criteria

• Warnings are shown when attempting to download from the old github container registry namespace
• Github downloads can be pulled from either github container registry namespace
• These updates are documented

Unit and Integration Tests

• Write or update any unit or integration tests