Add support to live-boot to support multiple read-only lower layers with overlayfs
_Originally created by @intrigeri on [#8473 (Redmine)](https://public-redmine-archive.tails.boum.org/code/issues/8473)_ Parent Task: tails/tails#8415 ### Related issues - [x] **Blocked by** tails/tails#8472 - [x] **Blocked by** tails/tails#8483 - **Blocks** tails/tails#9373
issue