Clean up known issues page, 4.0 edition

The known issues page should be updated to remove outdated data:
https://tails.boum.org/support/known_issues

The issues that are in tickets should also be added.

Feature Branch: doc/11665-clean-known-issues, https://salsa.debian.org/tails-team/tails/merge_requests/35

Related issues

• Related to #11687 (closed)
• Related to #11025 (closed)
• Related to #6551
• Related to #14505 (closed)
• Related to #14536
• Related to #15130
• Blocks #16711

Original created by @elouann on 11665 (Redmine)