title: Elasticsearch aggregation for each unit python
body: <p>I want for each unit (<code>org_name_en</code>) add a new field with aggregation for <code>review_count</code> - <code>sum / count</code>. Field <code>members</code> is a type of <code>nested</code>. Below you can see piece of ES db:</p>
  
  <pre><code>"hits" : [
        {
          "_index" : "some_index",
          "_type" : "_doc",
          "_id" : "some_id",
          "_score" : 1.0,
          "_source" : {
            "target_date" : "some_data",
            "org_name" : "abc",
            "org_name_en" : "ABC",
             [...]
            "members" : [
              {
                [...]
                "review_count" : 50.0,
              },
              {
                [...]
                "review_count" : 60.0,
              },
  </code></pre>
  
  <p>Final result should be like:</p>
  
  <pre><code>"hits" : [
        {
          [...]
          "_source" : {
            "target_date" : "filtered with some data",
            "org_name" : "abc",
            "org_name_en" : "ABC",
             [...]
            "members" : [
              {
                [...]
                "review_count" : 50.0,
              },
              {
                [...]
                "review_count" : 60.0,
              },
            ],
            "review_total": {
                  "review_sum": 110,
                  "review_count: 2
             },
           [...next unit DEF, GHI, XYZ with the same aggregation...]
  
  </code></pre>
  
  <p>My try with <strong>Elasticsearch-DSL</strong> in python - works only for given unit, so I need to filter it out first</p>
  
  <pre><code>qs.aggs.bucket('members', 'nested', path='members').metric('review_total', 'sum', field='members.review_count')
  </code></pre>