ci: add a ML model artifact test case

[rchincha]

Both as a test and an example.

Inspired by:
https://github.com/kubeflow/model-registry/blob/main/docs/logical_model.md

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What does this PR do / Why do we need it:

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.85%. Comparing base (8b4abc6) to head (4dfc69d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2332      +/-   ##
==========================================
- Coverage   92.86%   92.85%   -0.01%     
==========================================
  Files         167      167              
  Lines       22038    22038              
==========================================
- Hits        20465    20463       -2     
- Misses        981      982       +1     
- Partials      592      593       +1     

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[andaaron]

Earlier you had been using 'run regctl', was the content of 'lines' or 'output' variable not enough to get the shasum or index/manifest? Or why did you switch to using files?

[rchincha]

Earlier you had been using 'run regctl', was the content of 'lines' or 'output' variable not enough to get the shasum or index/manifest? Or why did you switch to using files?

When pulling the artifact, didn't want to hold it in a output var - could be very large.
The rest were removed first to verify output and later to make the usage uniform.