Install a desktop file for korgac

This is important for showing proper name and icon in the task manager on Wayland.

To avoid clashing with the existing autostart desktop file rename that one in source (but not the installed file)

This is like 7437e4bd but without the
string changes so we can get it into stable
2 jobs for !62 with work/backportdesktop in 1 minute and 32 seconds (queued for 1 second)
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