Support non-control driven field editing in SSP

[jpower432]

Issue description / feature objectives

Currently most of the support around SSP editing in markdown is for the control-implementation section. To reduce the amount of data edited through the JSON files, I propose we add support to edit non-control driven sections or fields in the SSP through a more user friendly option.

Caveats / Assumptions

This expands original project scope

Completion Criteria

• [ ] High-level design
• [ ] Clearly articulated set of issues with a forward looking plan on what fields to support. At minimum, the metadata and system-implementation fields

Proposed child Issues #1539

Community discussion about this Epic in Slack. Relevant GitHub community discussion - https://github.com/oscal-compass/compliance-trestle/discussions/1025