[Feature Request] Add v-model:grouped for VDataTable similar to v-model:expanded to easily access and interact with the groups.

[VandreiVer]

Problem to solve

Currently, you can enable default grouping on the VDataTable component by using the group-by property.
It would be nice to be able to double bind to them by using v-model, similar to how you can use v-model:expanded.
I imagine the functionality should be very similar.

In this way we could easily control which groups are expanded or not and significantly improve the developer experience if they want to add more interactivity.

Proposed solution

Provide the same functionality as v-model:expanded to grouped items ex: v-model:grouped which would hopefully expose the groups and their expanded/collapsed state.
Please see the following example

Thank you in advance! :)

[J-Sek]

related to #17707