Mz320 warmer integration test

[mzihlmann]

Fixes # in case of a bug fix, this should point to a bug and any other related issue(s)

Description

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Adds integration tests if needed.

See the contribution guide for more details.

Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

Release Notes

Describe any changes here so maintainer can include it in the release notes, or delete this block.

Examples of user facing changes:
- kaniko adds a new flag `--registry-repo` to override registry

[mzihlmann]

instead of adding a new test-case where we build from warmer, I think we should build from warmer per-default, as it improves the speed of our tests. And then we can modify the kaniko target to for example say that the test has to run in an air-gapped environment, to verify that warmer has worked properly.