no issue
- removed labs flag
- removed labs flag conditionals
- removed code related to old setup/done screen
- fixed tests that weren't correctly running against the GA flag code
refs
https://linear.app/tryghost/issue/IPC-92/add-logic-for-completing-steps
- added `onboarding` service to manage logic and state for the onboarding display and it's various steps
- added basic "display onboarding checklist" state to replicate the basic feature flag toggle along with making sure it's only shown to owners
- added acceptance test file and missing mirage endpoints needed for the dashboard to load without error