CDB-675 Add last_visualization_created_at metric
CDB-674 Track user first logins
Merge remote-tracking branch 'origin/feature/CDB-674' into release/2.3.2
* Mixpanel Log Event: User logins
Merge CDB-675 into release/2.3.2
* Mixpanel Log Event: Vizzs created and Last Vizz created