Add inventory-item-has-hardware-model Constraint

[Gabeblis]

Committer Notes

Purpose

This PR aims to add the inventory-item-has-hardware-model constraint which ensures that hardware model information is provided for hardware components / inventory items.

Changes

Added constraint:

• inventory-item-has-hardware-model

Added valid/invalid test content:

• ssp-inventory-item-has-hardware-model-INVALID.xml
• Edited fedramp-ssp-example.oscal.xml to align with constraint

Added yaml files for testing:

• Pass/fail yaml tests added for each of the above constraints.

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• If applicable, have all FedRAMP Documents Related to OSCAL Adoption affected by the changes in this issue have been updated.?
• If applicable, does this PR reference the issue it addresses and explain how it addresses the issue?

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