Add has-published-date constraint

[Gabeblis]

Committer Notes

Purpose

This PR introduces a validation constraint to ensure that each document submitted for FedRAMP authorization contains a valid publication date.

Changes

Constraint: has-published-date

• Validates that a published element exists.

Tests

• Added an invalid test data file for the above constraint.
• Added pass/fail YAML files for the above constraint to verify their functionality.

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  - [ ] If applicable, have all FedRAMP Documents Related to OSCAL Adoption affected by the changes in this issue have been updated.? No updates needed. Documentation exists.
• If applicable, does this PR reference the issue it addresses and explain how it addresses the issue?

By submitting a pull request, you are agreeing to provide this contribution under the CC0 1.0 Universal public domain dedication.

[kyhu65867]

Looks good to me