Support for script fields

[prugala]

Feature

Support for script fields

Merge _source with fields before denormalization process.

Creating script_fields in search result is stored in fields property e.g.:

Search object:

{
"script_fields": {
        "foo": {
            "script": {
                "source": "params._source.bar == 'test'",
            }
        },
}

Result:

"fields": {
                    "foo": [
                        true
                    ]
                }