add disjoint or difference (subtraction) to filter Groups

[pogojens]

Hey :)
It would be really nice if the "Toggle intersection/Toggle Union" button for filtering Groups could be extended by a disjoint funktion resulting in the functionality: Display all elements which are NOT in one of the selected Groups.

[ThiloteE]

Workaround for now: https://discourse.jabref.org/t/show-entries-without-group/492

[LoayGhreeb]

Will be implemented in #8963

[ThiloteE]

Closing, because is duplicate of #9073