Django Admin - Categorizing list_filter

### Code of Conduct

- [x] I agree to follow Django's Code of Conduct

### Feature Description

Idea is to be able to categorize list_filter, so filter can be grouped.

At moment it's just a list order dependend bunch of fields.

### Problem

At moment it's just a list order dependend bunch of fields.

On tables with many filters a specific filter is hard to be found, or will be overseen easily.

### Request or proposal

request

### Additional Details

_No response_

### Implementation Suggestions

I think a structure similar to fieldset grouping would be the best way.

For backward compatbility this should be an optional feature.

-> if a list_filter Element is a list or tuple, it's not a field, it's a categorized filter group

Implementation thought for django admin:

```
def get_list_filter(self, request):
return (
('Category A', {
fields: ['filter_a', 'filter_b', 'filter_c']}
),
('Category B', {
fields: ['filter_d', 'filter_e', 'filter_f']}
)
)
```

Start by tracing Django admin's get_list_filter/list_filter handling and compare it with the existing fieldset grouping behavior. Clarify the grouping structure, how it preserves the current list_filter format, and what admin rendering and tests would need to demonstrate that grouped filters work without breaking ungrouped filters.

Written by the indexing model from the issue text.