🐛 Fixed missing start date in members chart (#1644)
🐛 Fixed missing start date in members chart (#1644)

closes https://github.com/TryGhost/Ghost/issues/12014

- `startDateLabel` was never populated after refactoring the members chart to use the members stats service
- use the first date that's returned as part of the members stats days array so that we can account for any potential time period being selected

Co-authored-by: Kevin Ansfield <ffb4761cba839470133bee36aeb139f58d7dbaa9@lookingsideways.co.uk>
TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost