Create FedRAMP validations for SP 800-53 rev5 (source: 18F/fedramp-automation: 481)

[danielnaab]

Original issue: https://github.com/18F/fedramp-automation/issues/481

Extended Description

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

Preconditions

• #478 is complete.
• #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