Add Starfield support

[sapphiria39]

Hello, I'm pretty new to using GitHub so apologies if this isn't the right way of doing this.

I've added support for Starfield based on the comments here: #528

Since this requires MO2 v2.5.0, I added a mechanism for overriding the mo2_url via game_mo2_url in the gamesinfo scripts. It's also necessary to use Proton 9.0 (beta). And I needed to add a workaround for Data/SFSE/SFSE.ini to point to _Starfield.exe, similar to the Skyrim VR workaround.

I installed a handful of the popular mods and that all seemed to work. Would be good to have some others test it out as well.

It does feel a bit hacky to use game_mo2_url like this though, so I'm open to waiting until we've got the Proton 9 and MO2 v2.5.0 changes in place.

[rockerbacon]

The MO2 and Proton updates are two separate issues. #582 #543

Please include only the Starfield changes in this PR. You can submit separate PRs for updating MO2, as well as the recommended Proton version.

[sapphiria39]

Alright, I reverted the MO2 & Proton changes and re-tested the setup after merging latest.

[rockerbacon]

Thank you for your contribution!