Add Example SSP

[Gabeblis]

Committer Notes

Purpose

This PR aims to add a new example SSP.

Changes

• fedramp-example-ssp.xml was added to the content folder.
• feature file was edited to comment out ssp-all-VALID.xml under integration testing for now because future constraints will no longer be valid against this file as we shift towards using fedramp-example-ssp.xml.
• Test scaffolding function was edited in the dev-constraint.js file. A conditional statement was added that if the model is SSP, then point to the new fedramp-example-ssp.xml file. This preserves it's intended functionality for when we start writing constraints against other models, while also pointing to our new SSP example file when writing constraints against an SSP in the meantime.

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  - [ ] If applicable, have all FedRAMP Documents Related to OSCAL Adoption affected by the changes in this issue have been updated.? Not applicable.
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[aj-stein-gsa]

Per discussion while pairing earlier today, @wandmagic asked me to integrate the changes in #952 here, so I will work towards a PR to wrap in here.

[aj-stein-gsa]

Nice work, strong start. I have a general approach question/comment, but I can be happily overruled on that.