Add support for launching Beat Saber on Linux

[Insprill]

Scope

This PR adds support for launching Beat Saber on Linux.

Closes #441.

Implementation

A new application setting has been added, "Proton Path", which the user must specify before the game can be launched. This setting will only be shown to Linux users. When the game is launched, instead of running the Beat Saber executable directly, Proton will be run with the appropriate environment variables and arguments.

I'm still missing some Proton settings since there are a few bugs in Beat Saber I've run into when launching through BSManager that I haven't been able to reproduce when launching through Steam. Other than that, this is ready for a preliminary review. If there's anything you'd like me to implement differently please let me know :)

How to Test (Linux)

Note: Testing on Windows should also be done to ensure this PR doesn't cause any regressions.

• Set the Proton path in settings.
• Launch the game.

Emoji Guide

For reviewers: Emojis can be added to comments to call out blocking versus non-blocking feedback.

E.g: Praise, minor suggestions, or clarifying questions that don’t block merging the PR.

🟢 Nice refactor!

🟡 Why was the default value removed?

E.g: Blocking feedback must be addressed before merging.

🔴 This change will break something important

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[sonarqubecloud[bot]]

Quality Gate failed

Failed conditions
1 Security Hotspot

See analysis details on SonarCloud

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[Zagrios]

Thanks a lot ! 🎉🔥 Tested on windows and not problem 👌 @Insprill do you think that BSM is stable enough now on Linux to ship an AppImage? (not in production first of course, it will be shipped with the next alpha 😅)

[Insprill]

From my testing, yes! Everything is working fine on my system. I'll be happy to continue maintaining Linux support if (probably when :sweat_smile:) any issues pop up as well :)