Add support for OSCAL Shared Responsibilty Model

[jpower432]

Issue description / feature objectives

trestle currently supports the leveraged authorization use case for inheritance from one SSP to a leveraging SSP. This roadmap item captures a feature set around adding on to this functionality to support the OSCAL Shared Responsibility model.

Caveats / Assumptions

• Pending SRM prototype release

Completion Criteria

This is a roadmap item

• [ ] High-level design
• [ ] Clearly articulated set of issues per the plan

Supersedes #1378 Triggered by #1480