Support debugging XSpec and Schematron bugs

Extended Description As a knowledgable user or internal FedRAMP stakeholder, I would like to inspect the XSpec and Schematron for the validations, so I can study the logic and determine if there is a bug that requires fixing.

Context: when browsing the rules in the web documentation, a link to the corresponding lines of code on Github would aid the user in tracking down where the rule resides and how it is structured. For instance, a rule could include a link to the corresponding assertion, eg: https://github.com/GSA/fedramp-automation/blob/master/src/validations/rules/ssp.sch#L545-L551

Acceptance Criteria

[x] Docs link to Schematron assertion on Github
[x] Docs link to XSpec scenario on Github

Definition of Done

[x] Acceptance criteria met
[x] Unit test coverage of our code > 95%
[x] Automated code quality checks passed
[x] Security reviewed and reported
[x] Reviewed against plain language guidelines
[x] 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
[x] PR reviewed & approved
[x] Source code merged

18F / fedramp-automation

Support debugging XSpec and Schematron bugs #625