ElasticSearch integration

Revamp of  https://github.com/spiral-project/daybed/pull/173

Ready to merge or review !
I would have expected this to take the information it needs in the parameters, rather than unfolding them from the request.

But (yes, I think as I type) this seem to come at the cost of complexifying the code, just for the sake of a better separation of concerns.

If you think it's better to have this class completely tied to the notion of requests and the notion of events, then I think we should go for it. If the separation of concerns is easy to implement, maybe we should go for it :)