관련: .mapping 파일
참고: https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-source-field.html
The _source field contains
the original JSON document body
that was passed at index time.
The _source field is not indexed (is not searchable),
it can be returned when executing fetch requests, like get or search.
If disk usage is important
방법1. synthetic _source
방법2. disabling the _source field
일반적인 경우 이렇게 사용하는 것 같다
"_source": {
"enabled": true
},