Investigate whether we should ship /var/lib/systemd/random-seed

Originally created by @intrigeri on #7646 (Redmine)

See systemd-random-seed(8).

Blueprint: https://tails.boum.org/blueprint/randomness_seeding/

Related issues

• Related to #6116
• Related to #7675 (closed)
• Is duplicate of #7642 (closed)