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
closes https://github.com/TryGhost/Ghost/issues/12421
- added `emailOpenRate` property to member model
- added open-rate column to the members list
- hidden when email analytics is disabled
- added `{{feature "flag"}}` helper so feature flags can be checked in templates without injecting the feature service into the backing class
- added `order` query param to the members controller/route and wired it into the data fetching routine
- added order dropdown to the filter bar with "Newest" (default) and "Open rate" as the two options
- whole dropdown is hidden if email analytics is disabled
Co-authored-by: Kevin Ansfield <kevin@lookingsideways.co.uk>
