[Elasticsearch] Optimize the final query

[dkarlovi]

Q	A
Bug report?	no
Feature request?	yes
BC Break report?	no
RFC?	no

Currently, the final query generated for Elasticsearch is directly derived from the search condition. This can lead to verbose queries, for example for search condition name: foo you get:

{
    "query": {
        "bool": {
            "must": [
                {
                    "terms": {
                        "name": [
                            "foo"
                        ]
                    }
                }
            ]
        }
    }
}

Can be at least reduced to:

{
    "query": {
        "terms": {
            "name": [
                "foo"
            ]
        }
    }
}

We can also detect if we have exact or fuzzy matches and use filtered query (more examples of possible optimizations are linked).

[dkarlovi]

Note, we can also apply source filtering to reduce network IO.

[dkarlovi]

Also, we can deduce if the query is a "filter only" query and add a constant_score wrapper.