title: Jolt transformation to add a attribute to a JSON object
body: <p>I have two JSON objects as input and want to add a value of one object to the other.
  I have tried many different specs, but I can't get it to work. </p>
  
  <p>Here is an example of the situation:</p>
  
  <p>Input:</p>
  
  <pre><code>{
    "all": {
      "a": "1",
      "b": "2",
      "c": "3"
    },
    "partially": {
      "d": "4",
      "e": "5",
      "f": "6"
    }
  }
  </code></pre>
  
  <p>I want to have all data from the "all" object and I do not know what keys will be present. 
  On the other hand I know the keys of the "partially" object and I want to shift only selected.
  So for example here is a desired output:</p>
  
  <pre><code>{
    "result" : {
      "a" : "1",
      "b" : "2",
      "c" : "3",
      "d" : "4"
    }
  } 
  </code></pre>
  
  <p>This is my current spec, but it produces an array with separate data and does not select only "d" from the "partially". If I try to select only "d" it shifts the value but not the key, but I need both:</p>
  
  <pre><code>[
    {
      "operation": "shift",
      "spec": {
        "all": "result",
        "partially": "result"
      }
    }
  ]
  </code></pre>
  
  <p>Is there any way to do this?
  Thank you! </p>