Data Index EXPLAIN plan

## Use Case

> As a developer building on top of the hyper cloud and trying to debug performance issues with our indexes
> I want to utilize an `EXPLAIN` endpoint within the data API
> so that I can make sure that the indexes we expect are being used are actually being used.

## Notes

Requested by Travis Nesland.

Tom: I think a explain feature is a valid request and I believe many databases support an explain feature, I think we would need to be able to support a not implemented response as well for adapter implementers

Tyler: I agree with that. There are cases where an adapter might not implement an explain ie. sqlite adapter or something to that effect. Seems like the sort of thing that would be documented as a convention, then maybe a pre-canned util for adapter devs to use ie. NotImplementedHyperErr() or something.

No files, tests, or entry points are named. Start by locating the data API and its adapter interfaces, then determine how an EXPLAIN request and an adapter that does not support it should be represented. Done means the endpoint behavior and unsupported-adapter convention are defined and covered by appropriate tests.

Scritto dal modello di indicizzazione a partire dal testo della issue.