Update migration_style_guide.md with new details

What does this MR do?

Update the migration guide to include the necessary pieces to work.

Are there points in the code the reviewer needs to double check?

Are there any other critical updates? Does anything look incorrect?

Why was this MR needed?

The migration guide had incomplete information. It's likely that a bunch of stuff was updated in code but the docs weren't updated. Hopefully this brings it all up-to-date. Thanks for taking a look.