[meta] Onboarding optimisations

[rtestard]

User proposal

Optimize new user retention by helping users discover key capabilities that will help them keep using Focus after initial onboarding.

Ideas for Solution

We have identified 2 bodies of work to help drive new user retention and engagement through new user onboarding:

• Set to default
• Search Widget

The following separate issues are necessary to fulfill the delivery of this meta issue:

• [x] Update onboarding screen 1
• [x] Introduce onboarding screen 2
• [x] Replace "Go to Settings" CFR with "Start your private browsing session" CFR
• [x] Update the tracking protection CFR
• [x] Display the second onboarding tooltip on the first occurence of a site where Focus blocks trackers
• [x] Update trash can CFR
• [x] Introduce an onboarding step to promote widget addition
• [ ] Consider removal of old user onboarding
• [ ] Nimbus support for A/B testing the new onboarding
• [x] Telemetry requirements

Note: the iPad UX will use a modal sheet presentation style, similarly to current onboarding UX for iPad