Analytics: improve tracking of onboarding completed and login events

[ilmotta]

Problem

It is unreliable in the analytics tool to know which events actually represent a successful onboarding or a successful login. In particular for non-devs.

Acceptance Criteria

• onboarding-completed event is sent after a successful profile creation.
• user-logged-in event is sent after a successful login.
• Update Notion doc https://www.notion.so/Event-Tracking-Specification-Mobile-11a8f96fb65c8032a05efcebea3a1ce6#11a8f96fb65c802d9380e2de220e391e

As always, usage data collection is an opt-in feature.