Transition to a new signing key, phase 1

That’s what needs to go into Tails 1.3.

Feature Branch: feature/8739-new-signing-key-phase-1

Parent Task: #8222 (closed)

Subtasks

• #8729 (closed)
• #8731 (closed)
• #8738 (closed)
• #8732 (closed)

Related issues

• Blocks #8733 (closed)

Original created by @intrigeri on 8739 (Redmine)