Move role column from users table to user_details.onboarding_status

Move this into user_details.onboarding_status_role as a way to better group onboarding concerns.

• #498739 (comment 2227312475): Ensure data team is aware of this move in case they need to adjust any analysis of this data.
• !173777 (merged): Add new field to app/validators/json_schemas/user_detail_onboarding_status.json code that uses it/fills it. See #461404 (closed)
• Collect both fields temporarily per Data Team
• !175456 (merged): Backfilling/moving data for existing users.
• !177013 (merged): Cutover to the new field after backfill has finished.