Update system requirements for lizard failover

Our needs have changed quite a bit since we’ve specified these requirements 2 years ago (#6186 (closed)).

Blueprint: https://tails.boum.org/blueprint/lizard_failover/#system-specs

Parent Task: #6185 (closed)

Related issues

• Related to #6186 (closed)
• Related to #9400 (closed)
• Blocks #10244 (closed)

Original created by @intrigeri on 10243 (Redmine)