Create FedRAMP validations for SP 800-53 rev5

[GaryGapinski]

Extended Description

As a user of the FedRAMP validations, I would like to validate my documents against NIST RMF rev. 5 requirements.

Preconditions

• Create FedRAMP OSCAL content for SP 800-53 rev5 #478 is complete.
• Create FedRAMP/non-FedRAMP split #477 is complete.

Acceptance Criteria

• All Schematron assertion messages are declarative statements which affirm the positive test outcome.
• All Schematron assertion diagnostic messages are declarative statements which explain the negative test outcome.
• The Schematron code has no assertion failures when validated using src/validations/styleguides/sch.sch using the basic phase.
• XSpec unit tests for positive and negative Schematron assertion outcomes accompany all Schematron assertions (where feasible).
• More acceptance criteria…

Story Tasks

• Create Schematron validations for any rev5-specific novel constraints.

Definition of Done

• Acceptance criteria met
• Unit test coverage of our code > 95%
• Automated code quality checks passed
• Security reviewed and reported
• Reviewed against plain language guidelines
• Code must be self-documenting
• No local tech debt
• Load/performance tests passed – needs to be created/automated
• Documentation updated
• Architectural Decision Record completed as necessary for significant design choices
• PR reviewed & approved
• Source code merged