[Linux] Use Steam Runtime with Proton

[flavioislima]

Use SteamRuntime if available when using Proton.

• Check if soldier is available and use it
• if not, use scout

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Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)

[CommandMC]

runWineCommand also needs some changes to use the runtime there as well

[flavioislima]

@CommandMC I will leave the runWineCommand to another PR for now, but added a TODO for reminder.