[WIP] Rename 'Unpax' stage

Proposed changes

This PR addresses Issue: [Link to Github issue within https://github.com/zowe/zen/issues if any]

This PR depends upon the following PRs:

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[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Change in a documentation
[ ] Refactor the code
[ ] Chore, repository cleanup, updates the dependencies.
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

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[ ] If the changes in this PR are meant for the next release / mainline, this PR targets a "staging" branch.
[ ] My code follows the style guidelines of this project (see: Contributing guideline)
[ ] I have commented my code, particularly in hard-to-understand areas
[ ] I have made corresponding changes to the documentation
[ ] New and existing unit tests pass locally with my changes
[ ] video or image is included if visual changes are made
[ ] My changes generate no new warnings
[ ] I have added tests that prove my fix is effective or that my feature works, or describe a test method below