Warn on console when a generated migration contains reviewable steps

**Is your feature request related to a problem? Please describe.**

Destructive actions are commented out in generated migrations, but it's not clear to the user that something in the migration needs review.

**Describe the solution you'd like**

Ideally you should always review your migrations, but it'd be great to remind people of this with a note to this effect. Eg

`Please always manually review the generated migrations for correctness`

When there is something for review we should warn the user more emphatically to do so. Eg

`Warning: there are migration steps commented out and in need of manual review`