Recursive grouping

Hi,

I discover this terrific package since yesterday and now i'm testing different things to optimize my org workflow. So first, a big thanks for you works ! I'm happy to poste this 42 issue with a question about future functionality :)

I never jump into org-super-agenda / org-agenda because i don't use a day-by-day strict agenda for my work.
But, in parallel with org-roam Zettelkasten + part of PARA method, i maintain a lot of parallel projects tagged using `#+FILETAGS: :PROJECT:`, each in one separate org file.

```
/my-org-folder
| - index.org # refers all link to different projects, but also other area / ressources
| - myproject1.org
| - myproject2.org
| - xxx
```
Using org-ql-search i'm interested by creating a dashboard (one day using dynamic block with `:files` option :) ) with all TODO collected in my `projectxx.org`.

```
(let* ((files (->> (f--files "~/Notes/2ndBrain" (equal (f-ext it) "org")))))
(org-ql-search files
'(and (todo)
(tags "PROJECT"))
:super-groups '((:auto-category t))))
```

This first query return all TODO by filename, that a first step.
Ok, but now, if i want to display different subgroup view of TODO in this group ?

For example :
- displaying group by specific tag,
- displaying group by priority

I search example in the doc, but that seems not possible actually.

Do you plan something like that (grouping / recursive grouping) in the future for org-ql ?