fixes https://github.com/TryGhost/Team/issues/1821
This change moves all the event storage logic to one new place: the event storage class in the MembersEventsService, which is initialised in a new members events service wrapper.
Apart from this, this includes some improvements:
- Removed DomainEvents from the constructor arguments to the subscribe method (to make it more clear where to subscribe to and decrease dependencies)
- LastSeenAtUpdater doesn't subscribe in the constructor any longer (removes unclear side effect)
- Moved LastSeenAtUpdater initialisation to new members events service wrapper
- Added missing tests to LastSeenAtUpdater to assure that the MembersEventsService package has 100% coverage.
refs https://github.com/TryGhost/Team/issues/1306
- Contains all services that listen on member events
- Only contains the last-seen-at-updater service for now
- Listens for `MemberViewEvent` events to update the `member.last_seen_at` timestamp
- Updates after 24hours of the last timestamp to avoid too many writes
- Also updates when the value is NULL
- This is using the existing `last_seen_at` value to avoid an SQL query when no writes are required
