Transition USWDS Hugo theme to use Hugo Modules

[nikitawootten-nist]

User Story

As an OSCAL developer, I would like the Hugo site to be transitioned to Hugo modules in order to simplify CI/CD (and remove a submodule from the repository)

Goals

• All local CI/CD and local test infrastructure should be transitioned to rely on Hugo submodules
• The submodule should be removed
• A Wiki page or readme should be created explaining how to update the hugo module & stub a replacement for local theme development

Dependencies

No response

Acceptance Criteria

• 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.

[Arminta-Jenkins-NIST]

At 10/5 Triage Meeting: this issue is ready to be worked.