Update Documentation -> FedRAMP Extensions and Values Content

[Rene2mt]

As a developer, I want to update and rename the "Documentation->FedRAMP Extensions and Values" section content with proper reference to up-to-date FedRAMP registry.

Todo:

• Update registry to be "metaschema-based"
• Update registry to ensure it is comprehensive, listing all allowed values, and all extensions
• Update any links / references to the FedRAMP registry

#128 could replace the "Update registry ..." items above.

[Rene2mt]

@aj-stein-gsa and @brian-ruf, OSCAL-CLI now supports generating allowed values information in YAML format, directly from the model Metaschemas and our external constraints.

oscal-cli list-allowed-values results/fedramp-allowed-values-list.yaml -c constraints/fedramp-external-allowed-values.xml

This feature can be used in place of the experimental fedramp_values.xml (https://github.com/GSA/fedramp-automation/blob/master/dist/content/rev5/resources/xml/fedramp_values.xml).

Are there planned enhancements to the OSCAL-CLI that would allow us to list out all the FedRAMP extensions in a similar way?

Finally, how can we use these YAML outputs on the documentation site? I was thinking we could:

1. As part of CI, auto-generate an "Allowed-Values" page listing all (or just the FedRAMP-specific) allowed values - for example, there would be a markdown page at https://automate.fedramp.gov/documentation/allowed-values/ with formatted details of all the allowed values.
2. As part of CI, auto-generate a "FedRAMP Extensions" page listing all the FedRAMP extensions - for example, there would be a markdown page at https://automate.fedramp.gov/documentation/fedramp-extensions/ with formatted details of al the FedRAMP extensions
3. The other documentation pages, such as https://automate.fedramp.gov/documentation/ssp/4-ssp-template-to-oscal-mapping/#system-status, would provide deep links to the appropriate item in the pages above. This would hopefully make it easier for users to find because the information is consolidated in one page, and eliminate the need to have callouts throughout all the pages (like in the figure below).