emqx/v4.md at dev/api-refactor

Fixes

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

Added tests for the changes
Changed lines covered in coverage report
Change log has been added to changes/ dir
appup files updated (execute scripts/update-appup.sh emqx)
For internal contributor: there is a jira ticket to track this change
If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
In case of non-backward compatible changes, reviewer should check this item as a write-off, and add details in Backward Compatibility section