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
part of https://linear.app/tryghost/issue/IPC-92/add-logic-for-completing-steps
part of https://linear.app/tryghost/issue/IPC-115/make-skip-onboarding-button-work
- updated `onboarding` service to use the `user.accessibility` (poor naming, this is an old field used for general user settings) as it's backing store
- added `onboarding.allStepsCompleted` to allow for "completion" state to be shown before the checklist is marked as completed
- added `onboarding.{complete,dismiss}Checklist()` actions and wired those up to the template
When testing, if you need to reset the checklist you can run this in DevTools console
```
Ember.Namespace.NAMESPACES_BY_ID['ghost-admin'].__container__.lookup('service:onboarding').startChecklist()
```
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
