Add policy group 5 in Classroom baseline stating that only verified teachers can create classes

[jkaufman-mitre]

🗣 Description

Add policy group 5 in Classroom policy stating that only verified teachers can create classes.

Fixes #272

💭 Motivation and context

Public Comment

🧪 Testing

✅ Pre-approval checklist

• [x] This PR has an informative and human-readable title.
• [x] Changes are limited to a single goal - eschew scope creep!
• [x] If applicable, All future TODOs are captured in issues, which are referenced in the PR description.
• [x] The relevant issues PR resolves are linked preferably via closing keywords.
• [x] All relevant type-of-change labels have been added.
• [x] I have read and agree to the CONTRIBUTING.md document.
• [x] These code changes follow cisagov code standards.
• [x] All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• [x] Tests have been added and/or modified to cover the changes in this PR.
• [x] All new and existing tests pass.

✅ Pre-merge Checklist

• [x] This PR has been smoke tested to ensure main is in a functional state when this PR is merged.
• [x] Squash all commits into one PR level commit using the Squash and merge button.

✅ Post-merge Checklist

• [x] Delete the branch to clean up.
• [x] Close issues resolved by this PR if the closing keywords did not activate.

[jkaufman-mitre]

Ready for another review.

[adhilto]

I just added the needed code changes. I'll approve once you:

• Modify the policy name in the drift rule so it's the same as the md policy
• Add the pending TTP mapping

[jkaufman-mitre]

@adhilto I will work on getting the TTP mapping, but the drift rules file already has the correct policy statement.

[jkaufman-mitre]

@adhilto The TTP mappings have been added.