Airgap support for `baseImage` and `baseImageDocker`

[ChrisPbb]

Hello there! The functionality behind baseImage and baseImageDocker is not airgap-friendly because the container image URIs are not configurable. Listed below are the spots where container image URI is not configurable:

• Seemingly a placeholder container?
• kaniko builder
• luet utility
• generic util

Thanks for looking! 🔍 👀