Implement new allowed value design

[david-waltermire]

User Story

As an OSCAL developer or content creator, I need an easy way to understand which values are allowed to be used for a given data element within the OSCAL models.

The current OSCAL reference documentation lists the constraints that define the allowed values, but these constraints are often documented in a different location than where the value is used. This makes it very difficult to identify all of the allowed values for a given data element within the OSCAL models.

In issue #1337 a mockup of a new reference design was presented. As a follow-on, code needs to be written to produce allowed values using this representation.

Completing this issue will address the implementation in #1368.

Goals

• Write a documentation generator in Java that produces allowed values lists for each data element within the OSCAL models using the new representation.

Dependencies

This issue must be completed with the following issues.

• Disable Table of Contents on Pages #1372
• Add Linkage to Reference Entries and Outline #1371
• Add Breadcrumbing for Navigation #1370
• Flatten the Document Structure to Make the Page Load Faster #1369

Acceptance Criteria

• Consult with team and community to determine if the implementation is acceptable.
• All OSCAL website and readme documentation affected by the changes in this issue have been updated. Changes to the OSCAL website can be made in the docs/content directory of your branch.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.
• The CI-CD build process runs without any reported errors on the PR. This can be confirmed by reviewing that all checks have passed in the PR.

[aj-stein-nist]

Not completed last sprint and not in scope for Sprint 63, moving to the backlog.