Update image templating logic

[jumbosushi]

Description

• Specify repo package when using root-level images (e.g. from oci_pulls)
• Handle when image field in a yaml uses :image or @image labels
• Update image targets in container env vars for particular cases

Motivation and Context

Current templating logic missed some image use cases in Sciences.

How Has This Been Tested?

Tested with Sciences code

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.