Port CI/CD from CircleCI to GitHub Actions

[aj-stein-nist]

User Story:

As a NIST OSCAL developer working on the Metaschema project, to have effective continuous integration and continuous deployment be implemented and operated like the other OSCAL repositories, I would like that the CI/CD workflows in this repo be ported from CircleCI to GitHub Actions.

Goals:

• Align all repos with the same CI/CD tooling in OSCAL, not just the Metaschema repo (this is the remaining outlier)
• Facilitate reusable code across different GitHub Actions (CircleCI and GHA YAML are similar but not 1:1 identical and support it)
• Make sure the logical steps of the workflow in this repo align with the others and how they are structured in other OSCAL repos (build, verify build with validators, run unit tests, publish website on pages.nist.gov in a shareable way, not just similar CircleCI).

Dependencies:

N/A at this time.

Acceptance Criteria

• All previously defined steps in CircleCI will run successfully in GitHub Actions
• Necessary updates for documentation and design are documented for other team developers to troubleshoot and operate pipeline
• All website and readme documentation affected by the changes in this issue have been updated. Changes to the 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.

{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.}

[aj-stein-nist]

Per conversation during weekly sync with Dave on Monday and Friday's gameplan discussion summarized in #198 (comment), I am starting work on this now.