title: Dynamic options.addFields in beforeConstruct not working
body: <p>I was looking at creating a simple generic reusable text-only widget in apostrophe-cms so I made the module <code>text-only-widgets</code>.</p>
  
  <p>with the following code</p>
  
  <p><strong>In lib/modules/text-only-widgets/index.js</strong></p>
  
  <pre><code>module.exports = {
      extend: 'apostrophe-widgets',
      label: 'Section Heading',
  
      beforeConstruct: function (self, options) {
          console.log('options.addFields : ', options.addFields)
          options.addFields = [
              {
                  name: 'sectionHeading',
                  label: 'Section Heading',
                  type: 'string'
              }
          ].concat(options.addFields || [])
      }
  
  };
  </code></pre>
  
  <p><strong>In lib/modules/text-only-widgets/views/widget.html</strong></p>
  
  <pre><code>{{ data.widget.sectionHeading }}
  </code></pre>
  
  <p>Now I tried using the above widget in one of my pages as below:</p>
  
  <pre><code>  &lt;div&gt;
      {{
        apos.area(data.page, 'aboutUsDescriptionTwo', {
          widgets: {
            'text-only': {
            addFields: [
              {
                name: 'sectionDescription',  // set these fields dynamically
                label: 'Section Description',  // set these fields dynamically
                type: 'string'
              }
            ]
  
            }
          }
        })
      }}
    &lt;/div&gt;
  </code></pre>
  
  <p>As shown in the below image, notice even after passing the addFields with label as <strong>Section Description</strong> to the text-only widget doesn't override the defaults set in the index.js.</p>
  
  <p><a href="https://i.stack.imgur.com/zeULf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zeULf.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/X4PAV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/X4PAV.png" alt="enter image description here"></a></p>
  
  <p>I tried console.log on the options.addFields in index.js but it logs undefined as show below, I also tried few different variations but none works.</p>
  
  <p><a href="https://i.stack.imgur.com/t9Exb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/t9Exb.png" alt="enter image description here"></a></p>