This commit adds a new endpoint 'users/me/onboarding_steps'
deprecating the older 'users/me/hotspots' to mark hotspot as read.
We also renamed the view `mark_hotspot_as_read` to
`mark_onboarding_step_as_read`.
Reason: Our plan is to make this endpoint flexible to support
other types of UI elements not just restricted to hotspots.