Filter and return only specific fields using elasticsearch plugin with logstash

[Nico3 (Nicolas Chamberland)]

Hello,
I'm trying to create a pipeline with logstash in order to "extract" a specific metric from Elasticsearch (window_cpu_time_total). Here is my pipeline:

input {
  elasticsearch {
        hosts => ["http://localhost:9200"]
        index => "metricbeat-7.12.0-2021.04.29-000001"
        query => '{"_source": ["@timestamp", "labels","prometheus"]}'
      }
}
output {
      elasticsearch {
        hosts => ["http://localhost:9200"]
        index => "{test3[beat]}[version]}"
      }
    }

I get something like that which is closer to what I want. Now I would like an additional filter where I get only the metrics "prometheus.metrics.windows_cpu_time_total" and not the other metrics.

 {
"hits": {
    "hits": [
        {
        {
            "_source": {
                "@timestamp": "2021-04-29T15:35:57.518Z",
                "prometheus": {
                    "metrics": {
                        "windows_service_status": 0
                    },
                    "labels": {
                        "instance": "localhost:9182",
                        "name": "timebrokersvc",
                        "job": "prometheus",
                        "status": "lost comm"
                    }
                }
            }
        },
        {
            "_source": {
                "@timestamp": "2021-04-29T15:35:57.518Z",
                "prometheus": {
                    "metrics": {
                        "windows_cpu_time_total": 29480.625
                    },
                    "labels": {
                        "mode": "idle",
                        "core": "0,0",
                        "instance": "localhost:9182",
                        "job": "prometheus"
                    }
                }
            }
        }}]}}

Could someone help me with that ?
Thank you in advance