Enriching SP800-53A with links to statements

[wendellpiez]

User Story:

In view of a potential enhancement to OSCAL representation of SP800-53, we need to determine a preferred design.

#123 describes a potential data enhancement to SP800-53. A working branch includes a transformation that can make this enhancement: https://github.com/wendellpiez/oscal-content/tree/issue123-objectivelinks. That Issue also describes a couple of design options.

Unlike the enhancement offered in #86, adding links as described in #123 will not affect representation of artifacts, and can thus be made with no impact on questions of data fidelity. Data maintenance - keeping this information going forward in new versions of SP800-53 derived from upstream sources (that do not have these links) -- is potentially an issue, but not a blocking one.

Goals:

• Address questions raised by Add Linking from Objectives to Statements for the 800-53 Catalog #123 and make a determination on whether/how/when to proceed
• In doing so, brief community with options
• In doing so, review any decisions with NIST team

Dependencies:

While the policy question (whether we can do this) raised by #123 is not implicated here, there is still a maintenance question. Potentially this might be addressed by providing the enhancement logic in the conversion pipeline the next time it must be run.

Acceptance Criteria

• All readme documentation affected by the changes in this issue have been updated.
• 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.

{The items above are general acceptance criteria for all User Stories. Please describe anything else that must be completed for this issue to be considered resolved.}