Block internet access per game

[frostworx]

Might be nice to have an option to block internet/network access per game
The good old "sg no-internet" method I remember seems pretty much outdated, but some nice ideas are collected here
https://www.reddit.com/r/linux_gaming/comments/o9i58w/block_games_from_the_internet_with_firejail/
prepending a "unshare -n -r" (ships with util-linux) to the actual game command could as well,
but haven't tested anything yet.

[frostworx]

copy/paste of the (wip & offline) stl Block Internet wiki:

[Block Internet](https://github.com/frostworx/steamtinkerlaunch/wiki/Block Internet)

When enabling BLOCKINTERNET per game in Game Menu, stl
tries to block the internet access for the game by prepending
unshare -n -r to the game launch

You might want to read this if you have problems with the -r parameter

(when testing unshare-net via bwrap, the test game could not find its datafiles, so is hard-coded for now - feel free to submit a PR)

Of course, not every game works without internet access.

The option can also be enabled by putting the game into the BlockInternet Steam Category

[frostworx]

Added in release v6.13