Orchestration/scheduler/pre-cache

[greenape]

Because we don't allow any control over cache from FlowAPI, it would be desirable if a level of automatic pre-caching/scheduling/orchestration was applied to queries from that source.

There's quite a long way one can dive into this, but I think an initial approach which unrolls the query graph and does a traversal up it would be acceptable. I'd be inclined to say we want to be a little smart, and at least not trigger caching if there's no direct reason to do so for the outer query (i.e. query-to-return is an aggregate of a modal, modal is cached but daily aren't - right thing to do there is not to cache the daily).

I'd also be inclined to make this a behaviour that can be switched on or off via env var.