Docs: add missing items to migration guide #11628
What is the purpose of this pull request? (put an "X" next to item)
[x] Documentation update
What changes did you make? (Give an overview)
This updates the migration guide to add the missing items mentioned in #11515 (comment).
It does not add #9505 yet because there is some debate about whether that feature will still make it into the release.
Is there anything you'd like reviewers to focus on?