Add an option to set the console mode when using advanced mode for all lxc scripts

[mattague]

I regularly have to go in after lxc creation, and edit the options to change console mode to shell, for personal ease of use. It would be nice to be able to set this as a variable, maybe in the advanced settings, that gets passed to the build.func script, (I believe into the create_lxc_container() script specifically. This would be passed to the pct create command option --cmode. This allows users to set root passwords if wanted for security, while allowing WebUI console access to be login free similar to access the shell of proxmox, but still secure behind WebUI login, if wanted.

There's a perfect spot for it right next to the Template Storage. It could be set as a drop down with options for Default (tty), /dev/console, and shell. With a tooltip explaining that it is for the WebUI Console mode.