DM-47844: Add workflow that runs extra validation checks

[JeremyMcCormick]

• Addded a workflow that runs all extra validation checks
  • This does not run automatically. It needs to be triggered with workflow dispatch.
• Removed the old validator workflow and script
• Updated the existing validation workflow to use the test setup action
• Simplified the name of the main validation workflow to "Validate Schemas"

[gpdf]

This looks OK, but since apparently there's no way to actually execute it before it's merged, please merge this only when you feel you have time to do a followup if it doesn't work.