Add foreign keys to LiveAttempts

[FinnIckler]

This will fix the issue with orphaned attempts like #13208 and #13418

I currently have added deleting the orphaned result to the migration. Maybe we want to run this manually?

If we do run this first, we need to run both

      DELETE FROM live_attempt_history_entries
      WHERE live_attempt_id IN (
        SELECT id FROM live_attempts
        WHERE live_result_id IS NOT NULL
          AND live_result_id NOT IN (SELECT id FROM live_results)
      )

and

      DELETE FROM live_attempts
      WHERE live_result_id IS NOT NULL
        AND live_result_id NOT IN (SELECT id FROM live_results)

because there is currently no on_delete: cascade for the history entries