title: Transform { key: [values] } to {value: [keys]} in rego
body: <p>Please help me write a rule on <strong>rego</strong> that returns a transformed object.</p>
  <p>My object:</p>
  <pre><code>{
    &quot;read&quot;: [
      &quot;server1&quot;,
      &quot;server2&quot;
    ],
    &quot;write&quot;: [
      &quot;server2&quot;,
      &quot;server3&quot;
    ],
    &quot;create&quot;: [
      &quot;server1&quot;,
      &quot;server2&quot;,
      &quot;server3&quot;
    ]
  }
  </code></pre>
  <p>Expected:</p>
  <pre><code>{
    &quot;server1&quot;: [
      &quot;read&quot;,
      &quot;create&quot;
    ],
    &quot;server2&quot;: [
      &quot;read&quot;,
      &quot;write&quot;,
      &quot;create&quot;
    ],
    &quot;server3&quot;: [
      &quot;write&quot;,
      &quot;create&quot;
    ]
  }
  </code></pre>
  <p>I understand that I need to use comprehensions, but I don't understand how</p>