Importing external definitions of parties

[david-waltermire]

User Story:

As an OSCAL content creator, I need to import an external listing of parties into an OSCAL document. This allows the shared management of parties which can be reused across multiple documents.

Goals:

• Provide a mechanism to define a listing of parties in a seperate document.
• Provide an import mechanism, to import externally defined parties.

This relates to issue #590.

Dependencies:

None.

Acceptance Criteria

• All OSCAL website and readme documentation affected by the changes in this issue have been updated. Changes to the OSCAL website can be made in the docs/content directory of your branch.
• 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.

[david-waltermire]

This issue hasn't received any comments or support from the community. As a result, this issue is being moved to the backlog for future consideration.

[aj-stein-nist]

This most certainly needs deeper research than "Further Analysis Needed" scoping work in sprint to move forward, marking this as a potential issue for DEFINE. /cc @usnistgov/itl-oscal-define