Add support for "_source": false in Query when searching

[matus753]

My goal is to get all ids of records from Elastic using ReactiveElasticsearchTemplate.search filtered by NativeQuery. For that, I do not need to fetch source of the records.

I am not able to set that right now, I can only work around this by using:
.withSourceFilter(new FetchSourceFilterBuilder().withExcludes("*").build())
but that only generate SourceConfig with type Filter to exclude everything

I was wondering if it would be possible to add option for NativeQuery to set fetchSource(false)