add a version info file, that can be accessed by host for LXC Notes

[h00bi]

I would be nice if the installer and the update scripts would place a version info file somewhere inside the container.
Ideally same place vor every script.
Then we could use a host script via "pct enter" and write the current version to the LXC Notes.

For example with Jellyfin, run /usr/bin/jellyfin --version 2> version.txt at the end so we can access this file from the host.