Feature Request: Add "Rescue a broken system" feature from legacy Debian installer

[Victor Vavan]

In the previous debian installer (and the legacy focal installer -- https://cdimage.ubuntu.com/ubuntu-legacy-server/releases/20.04/release/) there is a useful "Rescue a broken system" feature which I would like to request be added to Subiquity.

This feature automatically mounts partitions and binds /dev, /proc, /sys followed by a chroot to the mountpoint. (Basically all the steps listed here: https://help.ubuntu.com/community/LiveCdRecovery#Update_Failure)

The legacy focal ISO, and this feature within it, is still frequently used by the Support team in order to bypass these initial steps when rescuing a system in a live troubleshooting call. Since the Support team does not have direct access to client systems, these steps prove to be cumbersome as they must be instructed to clients manually.