[Resolve #1503] Dependency conflict with packaging

[alex-harvey-z3q]

This restores the flexible constraints on packaging, allowing >=16.8 for compatibility with many old tools in the Sceptre ecosystem.

For example:
https://github.com/Sceptre/sceptre-aws-stackoutput-resolver/blob/master/requirements.txt#L6

PR Checklist

• Wrote a good commit message & description [see guide below].
• Commit message starts with [Resolve #issue-number].
• Added/Updated unit tests.
• Added/Updated integration tests (if applicable).
• All unit tests (poetry run tox) are passing.
• Used the same coding conventions as the rest of the project.
• The new code passes pre-commit validations (poetry run pre-commit run --all-files).
• The PR relates to only one subject with a clear title.
  and description in grammatically correct, complete sentences.

Approver/Reviewer Checklist

• Before merge squash related commits.

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[zaro0508]

this reverts PR #1495 which was intended to address issue #1478. Even with this revert, what if an install of sceptre happens to install packaging version >16.8 ? wouldn't that still break downstream dependencies? I have a feeling that the right thing to do here is to move forward.

[alex-harvey-z3q]

this reverts PR #1495 which was intended to address issue #1478.

It doesn't revert PR #1495, it restores the original version that I did of PR #1495. I believe the right thing to do here is merge this PR as soon as possible, otherwise latest Sceptre is broken for everyone in the world who tries to install any of our plugins along side of Sceptre. The other option would be to find and re-release every single plugin that has the 16.8 packaging dependency. That would take some time.