add auto-installer crate

add auto-installer crate

The new auto-installer is intended for unattended installations and
should be especially helpful for users with frequent and/or big
installations.

The main idea is that a answer file is provided by some mechanism,
e.g., on the ISO itself, on a separate (USB pen drive) partition, or
the network, which holds a somewhat generic config in form of a TOML
file that also supports wildcard glob'ing for selecting, e.g., target
disks for flexibility.

This is a initial implementation that will be improved and extended
over the next commits.

The installation config is currently generated through a dedicated
function (parse_answer) instead of a From implementation. This is
because for now the source data is spread over several other structs
in comparison to one in the TUI installer.

Logging is done to both stdout and a dedicated log file.

Tested-by: Christoph Heiss <c.heiss@proxmox.com>
Reviewed-by: Christoph Heiss <c.heiss@proxmox.com>
Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
 [ TL: Squash initial "build-up" patches ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>