Greeter revamp: Consider merging "basic" and "advanced" screens

From the feedback from experts (#8235 (closed)):

• Lot of screens [merge “Advanced configuration” and “1st screen”]

Feature Branch: https://tails.boum.org/blueprint/greeter_revamp_UI/design_rationale_phase1

Attachments

• 
• Content.Structure.Types.svgz

Parent Task: #8967 (closed)

Original created by @sajolida on 8976 (Redmine)