Add sandbox support

[kewde]

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Summarize your changes:
Adds support for --enable-sandbox, to be passed on to electron when executed.

[MarshallOfSound]

I think we're going to pass on this, you can already achieve this yourself with electron-forge start -- --enable-sandbox. If we add a custom flag for every Electron / Chromium / NodeJS option it will become unmanageable and we have to draw a line somewhere.