Add "disable_umu" as a global setting to avoid confusion

[gabriele2000]

Problem description

No response

Feature description

I've updated Heroic today and with horror I discovered that the option "disable_umu" is unchecked for all installed games.
I had to inspect the relevant PR to understand that the actual value is "undefined" and "tied to the previously existent experimental setting", that's not good from a "normal" user point of view.

Now there's no global option to disable it in Heroic's settings.
Reasons to not want umu in all games:

• I'd like to decide what components to install in a wineprefix
• Maybe a setting in umu-database is completely useless with future updates, I also like to use as little proprietary components as possible, even if that means waiting a month to fully play something
• Full control over what gets added to every prefix, maybe I'm using a specific .dll and I don't like when something breaks in a Windows OS style after an update.

Alternatives

The solution would be to put in settings->advanced the option "disable_umu" to enforce it globally.
The user could then disable that checkbox manually for every game.

Additional information

No response