Grouping description endpoint

[mathemancer]

Problem

Currently, we're not exposing hints about how different grouping methods work in the API, so we'd need to hard code some of that information in the front end to make it possible to use grouping to the fullest extent. We shouldn't have to hard code information about how different grouping modes work in the front end.

Proposed solution

We should use hints to give the front end information about how to use different grouping modes. This includes:

• needed arguments
• applicable types
• whether the grouping mode is ranged or not
• whether the grouping mode is multi-column or not

[mathemancer]

@dmos62 I think we can go back-and-forth in this issue about how this should look. Marking as draft until we have more details figured out (e.g., where the endpoint should go).