Add targets to mountpoint selection
Currently, there is no interactive way to mount a system on btrfs subvolumes. Also, there is no possibility of choosing entire devices in case someone wants to install in a partitionless setup.
Not sure what would be the best way to solve this. For partitionless options, we would only need to include the type disk. However, that may cause some confuseion for inexperienced users.
For mounting subvolumes... we could
A) list subvolumes with the lsblk output. This seems quite difficult, especially considering that subvolumes are visible only on mounted devices. B) If user selects a btrfs partition and does not format it, scan for subvolumes and offer to mount them instead.
B seems more viable at the moment