Hierarchical groups/Group sub-folders

[pcdi]

Is your feature request related to a problem? Please describe.
Since auto-grouping with metadata.toml makes it very easy to add a lot of groups, it can be annoying to sift through many groups before finding the one you are interested in.

Describe the solution you'd like
I think it would be nice if groups themselves could be grouped or if they could be ordered hierarchically (e.g. into folders). For example, I have some groups pertaining to the publishers of the dictionaries, some groups pertaining to the language(s) of the dictionaries and some groups pertaining to the type of dictionary (e.g. Thesaurus, collocation dictionary, etc.). If there is only one long list of groups, it takes more time to navigate than if there were subdivisions. For example, the "groups" drop-down menu in GD could have sub-menus, such as Groups > Publishers > Oxford or Groups > English > Collocations.

This sorting of groups into folders could either be done manually through the groups dialog in GD, or through some syntax in metadata.toml, e.g.:

categories = ["Publishers/Oxford", "English/Collocations"]

Describe alternatives you've considered
N/A

Additional context
N/A