Analyze early boot entropy gathering

Originally created by @sycamoreone on #11758 (Redmine)

One possibility to deal with the missing random seed would be to wait during the boot procedure until enough entropy has been gathered. We need to find out if that is actually possible and what consequences it would have.

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

Parent Task: #7642 (closed)

Related issues

• Related to #10779 (closed)
• Related to #5650 (closed)