Add Steam into the container

[BranislavF]

Hello,

please add Steam (with container workaround to be able to run Proton games).

Thank you

[ehfd]

Testers: Please try this and tell me before I add anything to the container.

Example of making Proton in Steam work without Pressure Vessel:

Assuming you have Proton Experimental installed in ~/.local/share/Steam/steamapps/common/Proton - Experimental, create ~/.local/share/Steam/compatibilitytools.d/Proton - Experimental (no runtime) and drop two files there, compatibilitytool.vdf that contains

"compatibilitytools"
{
  "compat_tools"
  {
    "proton_experimental_noruntime"
    {
      "install_path" "."
      "display_name" "Proton Experimental (no runtime)"
      "from_oslist"  "windows"
      "to_oslist"    "linux"
    }
  }
}

and toolmanifest.vdf with

"manifest"
{
  "version" "2"
  "commandline" "'/../../steamapps/common/Proton - Experimental/proton' %verb%"
}

[BranislavF]

So, after making a first mistake, by creating the folder elsewhere, I can confirm that it is working for me. At least the one game I tried. Using Proton Experimental (no runtime).

By the way, my steam installation folder was in ~/.steam/steam/ directory. Otherwise, it seems to be running ok :)

Thanks

[ehfd]

Then, we'll start incorporating when I have time.