Transition to a new signing key, phase 2

That’s what needs to go into Tails 1.3.1.

Feature Branch: feature/8740-new-signing-key-phase-2

Parent Task: #8222 (closed)

Subtasks

• #8730 (closed)
• #8734 (closed)
• #8735 (closed)
• #8736 (closed)
• #8769 (closed)
• #8882 (closed)

Related issues

• Blocks #8737 (closed)

Original created by @intrigeri on 8740 (Redmine)