fix: New cleanup when using --cleanup flag (#1406)

[mbenson]

Fixes #1406

Description

Rebase and re-push of #2783, requests for which the original author for unknown reasons did not satisfy.

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.

Reviewer Notes

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

Release Notes

Stage-dependent files are now removed from kaniko root directory after building the image, improving the reliability of multiple invocations of the kaniko executor in the same container.

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[mbenson]

The requests on the original PR were due to the CI/CD tests not kicking off, which still seems to be the case. Could this be due to the commit not including any test modifications?