Provide access to raw aggregations

[kardeiz]

#257 addresses the ability to work with additional aggregation types (I think).

I have a case where I am using cardinality aggs to calculate a count in ES, but this kind of aggregation can't be handled at all in the current system.

Even a simple fn raw_aggs(&self) -> Option<&::serde_json::Value> would be acceptable for the time being.

Also, somewhat off-topic, but what is the rationale for flattening typical "bucket" aggs as is done currently? It seems to break with ES conventions without offering any real benefits (in my opinion/as far as I can tell).

[KodrAus]

Yes, I've been meaning to generalise our support for aggregations. The original use-case was fairly specific for collecting metrics.

I think an aggs_raw method on SearchResponse that returns a Value is something we'll want to have, even in the future API where we'll keep aggs as Values internally.