Fix bugs in ExerciseMetadata for `fmt` command

This release fixes two fields in the exercises metadata in the track config.

1. Changes the type of the checklist_issue to an int (it's not a string)
2. Adds a boolean field, auto_approve. The v2 site has been operating with an assumption that it is there, defaulting to false where missing (which is everywhere). It also had a hack to set all the hello-world exercises to true in the database.