Make Tails Installer work fine outside of Tails

• add support for “install from ISO”
  • make sure “upgrade from ISO” works outside of Tails
  • create a tails-installer-launcher that only proposes these two options
  • refactor things as needed
  • also ship an amd64 syslinux binary in the ISO, otherwise Tails Installer will only work on 32-bit systems

Parent Task: #8549 (closed)

Subtasks

• #9381 (closed)
• #9574 (closed)
• #9594 (closed)
• #9378 (closed)
• #9379 (closed)
• #9380 (closed)

Related issues

• Has duplicate #8865 (closed)
• Blocked by #7046 (closed)
• Blocks #8557 (closed)
• Blocked by #8455 (closed)

Original created by @intrigeri on 8556 (Redmine)