Add option value for selecting the latest driver

[CodingKoopa]

I usually just want the latest regular driver, so, it would be nice if we could just set _driver_version to something like latest in the configuration file.

[Tk-Glitch]

Latest what? long-lived, short-lived, vulkan-dev? Date can be misleading due to legacy branches getting updates sometimes.

[CodingKoopa]

I'm afraid I don't understand Nvidia's release system much, but I suppose either latest short-lived or vulkan-dev depending on _driver_branch.