relates to #11669 Implements the UI for the end-user migration workflow. This includes: UI for migration form:  Preview payload modal:  Mdm setup state:  - [x] Changes file added for user-visible changes in `changes/` or `orbit/changes/`. See [Changes files](https://fleetdm.com/docs/contributing/committing-changes#changes-files) for more information. - [x] Manual QA for all new/changed functionality.