fix: show discrete GPU as default within cosmic context menu

[Jan200101]

requires pop-os/dbus-settings-bindings#29
matches pop-os/cosmic-launcher#399

Uses a discrete GPU when a more powerful GPU is requested using PrefersNonDefaultGPU

PrefersNonDefaultGPU
If true, the application prefers to be run on a more powerful discrete GPU if available, which we describe as “a GPU other than the default one” in this spec to avoid the need to define what a discrete GPU is and in which cases it might be considered more powerful than the default GPU. This key is only a hint and support might not be present depending on the implementation.

https://specifications.freedesktop.org/desktop-entry/latest/recognized-keys.html

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This PR could also do some more stuff like add a (discreted) / (dedicated) and how the GPU is selected could be tweaked, but that is best discussed in pop-os/cosmic-launcher#399

[jklgrasso]

The PR checklist is required

[Jan200101]

This PR predates the checklist, I'll add it in this comment:

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• I have disclosed use of any AI generated code in my commit messages.
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