OSCAL SSP: Separate and revise system owner and assignment of responsibility content

[brian-ruf]

User Story

As an implementer of tools for authoring of a FedRAMP SSP content, I need to understand the correct way to express the FedRAMP SSP system owner and assignment of responsibility details in OSCAL

Content Location

This content must reside in the Developer Hub as follows:

Repo Location:

/content/documentation/ssp/oscal-representation/owner-and-responsibility.md

URL Location:

https://automate.fedramp.gov/documentation/ssp/oscal-representation/owner-and-responsibility/

Revision Work Alignment

This content must align with the work performed in issue #805 :