Additional validations for rules

[jeeyyy]

Given, that we have some tests (#551) to validate the various sections of the rules (format & content), below are some enhancements to the tests that can be added.

• Ensure authors listed in frontmatter exist in contributors list in package.json.
• Check order of headings in rules.
• Check if all used glossary items, exist with in pages/glossary directory.

[jeeyyy]

@annethyme

• Feel free to expand on the above list, for additional validations that can be done to the rules.

Initial PR is here - #551

[jeeyyy]

Multiple tests in place, here is another #634. Closing.