[Enhancement] Header row & header group

[Phenek]

Summary

It would be nice to have a header for row and also for grouped rows
I mean header, like a top custom view with the size of the table's width.

Actual Behavior

We can expand or group row, but we can not have header on row or grouped rows.

Expected Behavior

The header of grouped rows could handle the expand functionality

Example

I did not found any workaround for this, that why I ask for an enhancement.
But if someone did this before. Please feel free to share, thanks in advance ;)