[KQL] Don't put KQL in filter but in Query

[timroes]

Currently when using KQL it will be put into a bool filter and not the query. Thus it's not possible to use KQL input for relevance matching and using it to get a good _score. We would like to improve scoring in Discover (e.g. by sorting by default by score if the user entered a query: #54362), but with KQL this does not work (while it did with Lucene).

I think the consumer of SearchSource.setField('query') should either have control over whether it will be put into filter or query, or always be put into query (and instead use setField('filter') for filters. I see a lot of use-cases where we might want to use KQL purely for filtering and never care about the score, thus I think it would be better to make it configurable by the consumer.

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)