title: Slack Dialog for search on external data source
body: <p>I have couple of question on slack dialog. I developed a form to complete and submit. One field is using external data source and I am able to see the options in the drop down. </p>
  
  <p>Further to enhance this, I would like to know if we can use a search functionality, like if the user types "abc", it show up on those options matching "abc". </p>
  
  <p>Another question which I have is, in the same form, having multiple fields, can we configure the dialog in such a way that, based on one value the other option set has to query and change. </p>
  
  <p>Please help on this part. Thank you. </p>
  
  <p>Dialog json using currently:</p>
  
  <pre><code>    {
          "label": "ProjectName",
          "type": "select",
          "name": "prjname",
          "data_source": "external",
      "min_query_length":3
      },
  </code></pre>