Support "Display field" in group-lists

[jamespohalloran]

Summary

Currently, when you have a group-list field, each entry is labelled as "X item", where X is the name of the group-list field. I would like the ability to configure a "display field", so that I can quickly distinguish between my entries

Basic example

It's currently a tedious process finding the list entry that I would like to edit. It also led to an editor issue, where my editor added a new entry, assumed it was added to the bottom of the list, and ended up editing the wrong entry.

Motivation

If I could configure the list to display each item's "title" field, this would be a much improved experience. Alternatively, maybe I could provide my own "render" function within the schema definition? (So that I could customize the list item to show an image for example?).
Maybe we also render the list-item's first field by default?

[DirtyF]

A common user request in Forestry was the ability to pick up the fields to display, for instance, when you use a group list for an image gallery, people expect to see a thumbnail in the list view.

[jeffsee55]

@DirtyF Instead of needing to manage this logic on the backend we could expose the frontend to our config, allowing us to leverage Tina as it works today with this pitch https://github.com/tinacms/product/discussions/13