Mount EPHEMERAL volume via new controller.
Implement the first cut of volume dependencies from services, refactor
the way system disk wipe works.
Update volume manager controller to destroy volume statuses on shutdown,
which allows to signal mount operations to be terminated.
Lots of WIP ideas still, but I want to complete this PR and move on to
the next one:
* refactor user disks mounts to use new API
* refactor STATE mountes to use new API
* implement directory/overlay mounts
Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>
