Datapoint graph support #4892

I would like to be able to..

Get a graph for any Datapoint that supports it

Is your feature request related to a problem? Please describe.

The current graph endpoint is quite rigid, it would be nice to be able to fetch points between two date values.

In addition to this, I want to make it easier to add graphs of existing stuff, not necessarily sampled data, but computed where possible.

It would be easy to define an additional interface for Datapoint and programmatically find out which points support graphs, and just show a little button next to them that gets the graph.

This way the graph can be defined in a single query rather than needing to write query, endpoint, and visualization