title: move json fields to root - logstash
body: <p>my logs contain nested json under <code>det</code> field</p>
  
  <pre><code>{
          "id" =&gt; "1234",
          "@version" =&gt; "1",
          "@timestamp" =&gt; "2015-05-27T03:45:33.094Z",
          "det" =&gt; {
                      "name" =&gt; "jim",
                      "a" =&gt; "11111",
                      "b" =&gt; "222222",
                      "c" =&gt; "33333"
          }
  }
  </code></pre>
  
  <p>I would like to move all keys under <code>det</code> to root. (dynamically, without the need to mention child key names)</p>
  
  <p><strong>result:</strong></p>
  
  <pre><code>{
          "id" =&gt; "1234",
          "@version" =&gt; "1",
          "@timestamp" =&gt; "2015-05-27T03:45:33.094Z",
          "name" =&gt; "jim",
          "a" =&gt; "11111",
          "b" =&gt; "222222",
          "c" =&gt; "33333"
  
  }
  </code></pre>
  
  <p>what filter can I use?</p>