Group rows API

Hi there!

We're from Streak (yc s11) and we're looking to move to Glide Data Grid. One missing feature from our current in-house implementation is the ability to have group rows.

Here's roughly what we mean by a group row (notice all the features are listed in the screenshot):

Here's a video of how the group row interactions feel wrt to scrolling and selection: https://www.loom.com/share/6cdaabf0bc3f402c90099749f2d65ada

Would love to start the discussion on how this might be implemented in GDG, we'd be happy to implement.